glocalfileinfo: Stop using PATH_MAX for .hidden

glocalfileinfo: Stop using PATH_MAX for .hidden

We were using PATH_MAX to size a static array for reading lines from
the .hidden file.  Some platforms (Hurd) don't declare a PATH_MAX.

Switch to using g_file_get_contents() and g_str_split('\n') instead.

Also take the time to clean up a bit with a switch to using a 'set mode'
GHashTable (since this code was originally written before we had those).

This patch is largely based on a patch from Emilio Pozuelo Monfort (who
also reported the bug).

https://bugzilla.gnome.org/show_bug.cgi?id=695147