ENH: Simplify decision to use system libraries

Previously we disallowed use of system libraries if FindXMLRPC.cmake was
not available.  Now that CMake 2.4 is required to build, the module is
always available.  This change simplifies the logic accordingly.

CMakeLists.txt

@@ -13,59 +13,44 @@ MARK_AS_ADVANCED(CMAKE_BACKWARDS_COMPATIBILITY)
 # simply to improve readability of the main script
 #-----------------------------------------------------------------------
 MACRO(CMAKE_HANDLE_SYSTEM_LIBRARIES)
-  # Third party libraries must be something that can be found.
-  IF(EXISTS ${CMAKE_ROOT}/Modules/FindXMLRPC.cmake)
-    SET(CMAKE_ALLOW_SYSTEM_LIBRARIES 1)
-  ELSE(EXISTS ${CMAKE_ROOT}/Modules/FindXMLRPC.cmake)
-    SET(CMAKE_ALLOW_SYSTEM_LIBRARIES 0)
-  ENDIF(EXISTS ${CMAKE_ROOT}/Modules/FindXMLRPC.cmake)
-  
-  IF(CMAKE_ALLOW_SYSTEM_LIBRARIES)
-    # Options have dependencies.
-    INCLUDE(CMakeDependentOption)
-    
-    # Allow the user to enable/disable all system utility library options
-    # by setting CMAKE_USE_SYSTEM_LIBRARIES on the command line.
-    IF(DEFINED CMAKE_USE_SYSTEM_LIBRARIES)
-      SET(CMAKE_USE_SYSTEM_LIBRARIES_USER 1)
-    ENDIF(DEFINED CMAKE_USE_SYSTEM_LIBRARIES)
-    IF(CMAKE_USE_SYSTEM_LIBRARIES)
-      SET(CMAKE_USE_SYSTEM_LIBRARIES ON)
-    ELSE(CMAKE_USE_SYSTEM_LIBRARIES)
-      SET(CMAKE_USE_SYSTEM_LIBRARIES OFF)
-    ENDIF(CMAKE_USE_SYSTEM_LIBRARIES)
-    IF(CMAKE_USE_SYSTEM_LIBRARIES_USER)
-      SET(CMAKE_USE_SYSTEM_CURL "${CMAKE_USE_SYSTEM_LIBRARIES}" 
-        CACHE BOOL "Use system-installed curl" FORCE)
-      SET(CMAKE_USE_SYSTEM_EXPAT "${CMAKE_USE_SYSTEM_LIBRARIES}" 
-        CACHE BOOL "Use system-installed expat" FORCE)
-      SET(CMAKE_USE_SYSTEM_XMLRPC "${CMAKE_USE_SYSTEM_LIBRARIES}" 
-        CACHE BOOL "Use system-installed xmlrpc" FORCE)
-      SET(CMAKE_USE_SYSTEM_ZLIB "${CMAKE_USE_SYSTEM_LIBRARIES}" 
-        CACHE BOOL "Use system-installed zlib" FORCE)
-    ENDIF(CMAKE_USE_SYSTEM_LIBRARIES_USER)
-    
-    # Optionally use system utility libraries.
-    OPTION(CMAKE_USE_SYSTEM_CURL   "Use system-installed curl" 
-      ${CMAKE_USE_SYSTEM_LIBRARIES})
-    OPTION(CMAKE_USE_SYSTEM_XMLRPC "Use system-installed xmlrpc" 
-      ${CMAKE_USE_SYSTEM_LIBRARIES})
-    CMAKE_DEPENDENT_OPTION(CMAKE_USE_SYSTEM_EXPAT "Use system-installed expat"
-      ${CMAKE_USE_SYSTEM_LIBRARIES} "NOT CMAKE_USE_SYSTEM_XMLRPC" ON)
-    CMAKE_DEPENDENT_OPTION(CMAKE_USE_SYSTEM_ZLIB "Use system-installed zlib"
-      ${CMAKE_USE_SYSTEM_LIBRARIES} "NOT CMAKE_USE_SYSTEM_CURL" ON)
-    
-    # There is currently no option for system tar because the upstream
-    # libtar does not have our modifications to allow reentrant
-    # object-oriented use of the library.
-    # OPTION(CMAKE_USE_SYSTEM_TAR    "Use system-installed tar"   OFF)
-  ELSE(CMAKE_ALLOW_SYSTEM_LIBRARIES)
-    SET(CMAKE_USE_SYSTEM_CURL 0)
-    SET(CMAKE_USE_SYSTEM_EXPAT 0)
-    SET(CMAKE_USE_SYSTEM_XMLRPC 0)
-    SET(CMAKE_USE_SYSTEM_ZLIB 0)
-  ENDIF(CMAKE_ALLOW_SYSTEM_LIBRARIES)
-
+  # Options have dependencies.
+  INCLUDE(CMakeDependentOption)
+
+  # Allow the user to enable/disable all system utility library options
+  # by setting CMAKE_USE_SYSTEM_LIBRARIES on the command line.
+  IF(DEFINED CMAKE_USE_SYSTEM_LIBRARIES)
+    SET(CMAKE_USE_SYSTEM_LIBRARIES_USER 1)
+  ENDIF(DEFINED CMAKE_USE_SYSTEM_LIBRARIES)
+  IF(CMAKE_USE_SYSTEM_LIBRARIES)
+    SET(CMAKE_USE_SYSTEM_LIBRARIES ON)
+  ELSE(CMAKE_USE_SYSTEM_LIBRARIES)
+    SET(CMAKE_USE_SYSTEM_LIBRARIES OFF)
+  ENDIF(CMAKE_USE_SYSTEM_LIBRARIES)
+  IF(CMAKE_USE_SYSTEM_LIBRARIES_USER)
+    SET(CMAKE_USE_SYSTEM_CURL "${CMAKE_USE_SYSTEM_LIBRARIES}"
+      CACHE BOOL "Use system-installed curl" FORCE)
+    SET(CMAKE_USE_SYSTEM_EXPAT "${CMAKE_USE_SYSTEM_LIBRARIES}"
+      CACHE BOOL "Use system-installed expat" FORCE)
+    SET(CMAKE_USE_SYSTEM_XMLRPC "${CMAKE_USE_SYSTEM_LIBRARIES}"
+      CACHE BOOL "Use system-installed xmlrpc" FORCE)
+    SET(CMAKE_USE_SYSTEM_ZLIB "${CMAKE_USE_SYSTEM_LIBRARIES}"
+      CACHE BOOL "Use system-installed zlib" FORCE)
+  ENDIF(CMAKE_USE_SYSTEM_LIBRARIES_USER)
+
+  # Optionally use system utility libraries.
+  OPTION(CMAKE_USE_SYSTEM_CURL   "Use system-installed curl"
+    ${CMAKE_USE_SYSTEM_LIBRARIES})
+  OPTION(CMAKE_USE_SYSTEM_XMLRPC "Use system-installed xmlrpc"
+    ${CMAKE_USE_SYSTEM_LIBRARIES})
+  CMAKE_DEPENDENT_OPTION(CMAKE_USE_SYSTEM_EXPAT "Use system-installed expat"
+    ${CMAKE_USE_SYSTEM_LIBRARIES} "NOT CMAKE_USE_SYSTEM_XMLRPC" ON)
+  CMAKE_DEPENDENT_OPTION(CMAKE_USE_SYSTEM_ZLIB "Use system-installed zlib"
+    ${CMAKE_USE_SYSTEM_LIBRARIES} "NOT CMAKE_USE_SYSTEM_CURL" ON)
+
+  # There is currently no option for system tar because the upstream
+  # libtar does not have our modifications to allow reentrant
+  # object-oriented use of the library.
+  # OPTION(CMAKE_USE_SYSTEM_TAR    "Use system-installed tar"   OFF)
 
   # Mention to the user what system libraries are being used.
   FOREACH(util CURL EXPAT XMLRPC ZLIB)