CheckIncludeFiles: Shorten check description message

Since commit 44d007b6 (CheckIncludeFiles: fix status output, 2012-02-01)
check_include_files reports the list of files tested instead of the name
of the variable storing the result.  Some projects incrementally test
and concatenate very long lists leading to long messages that do not
provide much information.  Users report confusion especially when the
lines wrap.

For lists of more than two files produce messages of the format

 Looing for N include files first.h, ..., last.h

where N is the list length and "..." is literal.  Leave the log file
entries and cache entry description unchanged as they should have the
full detail of the check performed.

Modules/CheckIncludeFiles.cmake

@@ -13,7 +13,7 @@
 #  CMAKE_REQUIRED_INCLUDES = list of include directories
 
 #=============================================================================
-# Copyright 2003-2009 Kitware, Inc.
+# Copyright 2003-2012 Kitware, Inc.
 #
 # Distributed under the OSI-approved BSD License (the "License");
 # see accompanying file Copyright.txt for details.
@@ -44,7 +44,17 @@ MACRO(CHECK_INCLUDE_FILES INCLUDE VARIABLE)
     CONFIGURE_FILE("${CMAKE_ROOT}/Modules/CMakeConfigurableFile.in"
       "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/CheckIncludeFiles.c" @ONLY IMMEDIATE)
 
-    MESSAGE(STATUS "Looking for include files ${INCLUDE}")
+    SET(_INCLUDE ${INCLUDE}) # remove empty elements
+    IF("${_INCLUDE}" MATCHES "^([^;]+);.+;([^;]+)$")
+      LIST(LENGTH _INCLUDE _INCLUDE_LEN)
+      SET(_description "${_INCLUDE_LEN} include files ${CMAKE_MATCH_1}, ..., ${CMAKE_MATCH_2}")
+    ELSEIF("${_INCLUDE}" MATCHES "^([^;]+);([^;]+)$")
+      SET(_description "include files ${CMAKE_MATCH_1}, ${CMAKE_MATCH_2}")
+    ELSE()
+      SET(_description "include file ${_INCLUDE}")
+    ENDIF()
+
+    MESSAGE(STATUS "Looking for ${_description}")
     TRY_COMPILE(${VARIABLE}
       ${CMAKE_BINARY_DIR}
       ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/CheckIncludeFiles.c
@@ -54,14 +64,14 @@ MACRO(CHECK_INCLUDE_FILES INCLUDE VARIABLE)
       "${CHECK_INCLUDE_FILES_INCLUDE_DIRS}"
       OUTPUT_VARIABLE OUTPUT)
     IF(${VARIABLE})
-      MESSAGE(STATUS "Looking for include files ${INCLUDE} - found")
+      MESSAGE(STATUS "Looking for ${_description} - found")
       SET(${VARIABLE} 1 CACHE INTERNAL "Have include ${INCLUDE}")
       FILE(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log 
         "Determining if files ${INCLUDE} "
         "exist passed with the following output:\n"
         "${OUTPUT}\n\n")
     ELSE(${VARIABLE})
-      MESSAGE(STATUS "Looking for include files ${INCLUDE} - not found.")
+      MESSAGE(STATUS "Looking for ${_description} - not found.")
       SET(${VARIABLE} "" CACHE INTERNAL "Have includes ${INCLUDE}")
       FILE(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log 
         "Determining if files ${INCLUDE} "