Make the search entry behave better in RTL locales

It is expected that the primary and secondary icons in entries
change places in RTL locales. When doing so, the edit-clear
icon must be replaced by an rtl variant too.

http://bugzilla.gnome.org/show_bug.cgi?id=705779
st: Fix spacing on right icon in entry

https://bugzilla.gnome.org/show_bug.cgi?id=705779