Fix typo in .pc file

Requires.Private should be Requires.private.

https://bugzilla.gnome.org/show_bug.cgi?id=721719
Do not overwrite text attributes with the default ones

As it was implemented, the default attributes are appended to the end
of the list, and later in time only the last occurence of every
attribute will be preserved.

Just changing the order of the list fixes this bug.

https://bugzilla.gnome.org/show_bug.cgi?id=731980
Correctly remove the socket on exit

https://bugzilla.gnome.org/show_bug.cgi?id=684076
Release v2.13.4