pidgin/pidgin

Fix up the dependencies for our gir files and ensure ours will work as a subproject

Testing Done:
Tested against gplugin 0.34.1 and everything is working well.

Reviewed at https://reviews.imfreedom.org/r/942/
nullclient = executable('nullclient', 'nullclient.c', 'defines.h',
c_args : ['-DSTANDALONE'],
dependencies : [libpurple_dep, glib])