auric: Use g_mkdir_with_parents() instead of our own version

Replace our mkdir_p() with GLib's g_mkdir_with_parents(), might as well
use what we already have available to use and gives a nice little code
reduction.

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>
src/auric.c: Open the config file with the O_CLOEXEC flag

Use the 'e' flag in the fopen(3) syscall in load_prefs().

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>
src/auric.c: Open the data file with the O_CLOEXEC flag

Use the 'e' flag in the fopen(3) syscall in read_tmpl().

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>