libgnt/libgnt

Define G_LOG_DOMAIN during our build so our logs will show where the come from.

Testing Done:
Built and ran a few of the manual tests.

Reviewed at https://reviews.imfreedom.org/r/191/
plugindir = get_option('libdir') / 'gnt3'
irssi = library('irssi', 'irssi.c',
dependencies : [ncurses, gobject, libgnt_dep],
name_prefix : '',
install : true, install_dir : plugindir)
s = library('s', 's.c',
dependencies : [ncurses, gobject, libgnt_dep],
name_prefix : '',
install : true, install_dir : plugindir)