(gtk) use replace strcmp() with g_strcmp0() everywhere

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14018 f4695dd4-2c0a-0410-b89c-da849a56a58e
(qt) #5278 'Something strange with the color of progress bars' -- patch by rb07

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14019 f4695dd4-2c0a-0410-b89c-da849a56a58e
(libT) #5293 'Wrong error codes used in upnp.c': patch by rb07

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14020 f4695dd4-2c0a-0410-b89c-da849a56a58e