Both GFLAGS_NAMESPACE and GFLAGS_INCLUDE_DIR can be used to customize the installation of the gflags library. One specifies the C++ namespace name of the gflags symbols, the other the include subdirectory path of the public header files. By default, both are set to "gflags", but other Google libraries still expect "google" as C++ namespace name, but not necessarily also include path.

Conflicts:
	gflags-vs2003.sln
	gflags-vs2010.sln
	gflags-vs2012.sln
	vsprojects/gflags_unittest/gflags_unittest-vs2010.vcxproj
	vsprojects/libgflags/libgflags-vs2010.vcxproj

Change version to 2.1.0, i.e., use common semantic versioning system including patch number for bug fix releases.

This reverts commit fb21f3cc.

Add link dependency on shlwapi.lib during build configuration instead of #pragma comment statement. Use this library also on MinGW.

The OS_WINDOWS #define has previously been used in gflags.cc before the CMake migration.