bootstrap: Add --(no-)system-jsoncpp options

Provide bootstrap-time control for using a system JsonCpp library.

bootstrap

@@ -398,6 +398,8 @@ Configuration:
   --no-system-curl        use cmake-provided curl library (default)
   --system-expat          use system-installed expat library
   --no-system-expat       use cmake-provided expat library (default)
+  --system-jsoncpp        use system-installed jsoncpp library
+  --no-system-jsoncpp     use cmake-provided jsoncpp library (default)
   --system-zlib           use system-installed zlib library
   --no-system-zlib        use cmake-provided zlib library (default)
   --system-bzip2          use system-installed bzip2 library
@@ -637,10 +639,10 @@ while test $# != 0; do
   --init=*) cmake_init_file=`cmake_arg "$1"` ;;
   --system-libs) cmake_bootstrap_system_libs="${cmake_bootstrap_system_libs} -DCMAKE_USE_SYSTEM_LIBRARIES=1" ;;
   --no-system-libs) cmake_bootstrap_system_libs="${cmake_bootstrap_system_libs} -DCMAKE_USE_SYSTEM_LIBRARIES=0" ;;
-  --system-bzip2|--system-curl|--system-expat|--system-libarchive|--system-zlib)
+  --system-bzip2|--system-curl|--system-expat|--system-jsoncpp|--system-libarchive|--system-zlib)
     lib=`cmake_arg "$1" "--system-"`
     cmake_bootstrap_system_libs="${cmake_bootstrap_system_libs} -DCMAKE_USE_SYSTEM_LIBRARY_`cmake_toupper $lib`=1" ;;
-  --no-system-bzip2|--no-system-curl|--no-system-expat|--no-system-libarchive|--no-system-zlib)
+  --no-system-bzip2|--no-system-curl|--no-system-expat|--no-system-jsoncpp|--no-system-libarchive|--no-system-zlib)
     lib=`cmake_arg "$1" "--no-system-"`
     cmake_bootstrap_system_libs="${cmake_bootstrap_system_libs} -DCMAKE_USE_SYSTEM_LIBRARY_`cmake_toupper $lib`=0" ;;
   --qt-gui) cmake_bootstrap_qt_gui="1" ;;