More sensible defaults and allow for overriding. Also make PDB installation
optional on Windows if RelWithDebInfo isn't the build type being used.
CMAKE_INSTALL_PREFIX defaults to GStreamer install location on Windows and
/usr/lib on other platforms.
PLUGIN_INSTALL_DIR defaults to CMAKE_INSTALL_PREFIX/gstreamer-1.0
LIBRARY_INSTALL_DIR defaults to CMAKE_INSTALL_PREFIX/
PDB_INSTALL_DIR defaults to CMAKE_INSTALL_PREFIX/
Merged from https://github.com/zingmars/gst-pylonsrc
This includes some changes to include running gst-indent, and
modification to allow it to compile with Visual Studio 2012/VC11.
