Classic mode should be visually distinct from the normal session,
so provide a mode-specific stylesheet which looks closer to the
familiar GNOME2 default theme.
https://bugzilla.gnome.org/show_bug.cgi?id=693169
With new items being added on the left, the top bar gets a little
crowded with the dateMenu at the center, so move it to its "classic"
position on the right.
https://bugzilla.gnome.org/show_bug.cgi?id=692016
The Makefile had two rules by which it could possibly have generated the
intermediate .in file (on the way from .in.in to .session) and it picked
the one that didn't contain the substitution for @libexecdir@.
Consolidate the rules into one that does all the needed substitutions.
https://bugzilla.gnome.org/show_bug.cgi?id=689756
