COMP: Jsoncpp ignores BUILD_SHARED_LIBS.

Instead it uses JSONCPP_LIB_BUILD_SHARED internally.
Merge pull request #236 from ricortiz/jsoncpp-ignores-shared

COMP: Jsoncpp ignores BUILD_SHARED_LIBS.
COMP: Move inclusion of fPIC flag to CMakeLists.txt in superbuild dir
Merge pull request #237 from aylward/fPICConsolidation

COMP: Move inclusion of fPIC flag to CMakeLists.txt in superbuild dir