Fixed building Evolution add-in on Ubuntu 12.04
Fixed building Evolution add-in on Ubuntu 12.04

...and most probably other Debian-based systems with gmime-sharp 2.6

Signed-off-by: Jared Jennings <ad0460cb04d67eb39a9c46471c88e93819177116@src.gnome.org>

tomboy-notes/tomboy,rotty3000/tomboy,rotty3000/tomboy,tomboy-notes/tomboy,rotty3000/tomboy,rotty3000/tomboy,tomboy-notes/tomboy,MatteoNardi/Tomboy,MatteoNardi/Tomboy,rotty3000/tomboy,MatteoNardi/Tomboy,tomboy-notes/tomboy,MatteoNardi/Tomboy,MatteoNardi/Tomboy,MatteoNardi/Tomboy,tomboy-notes/tomboy