pidgin/pidgin

Change the introspection option to a boolean so that the subprojects can properly yield to it.

Testing Done:
ninja reconfigure to verify that the error about not being able to yield went away.

Reviewed at https://reviews.imfreedom.org/r/150/
libpurple/data/purple-url-handler.desktop.in
libpurple/protocols/null/nullprpl.c
pidgin/data/im.pidgin.Pidgin.desktop.in
sub/libpurple/data/purple-url-handler.desktop.in
sub/libpurple/protocols/null/nullprpl.c
sub/pidgin/data/im.pidgin.Pidgin.desktop.in