dia.doap: add description and progamming languages
[gtk-osx] Don't quit without asking to save files first

i.e. connect the exisiting method to an OS X specific signal
[gtk-osx] Improve modifier handling for dragging handles

Kludge against GTK/Quartz returning bogus values,
see https://bugzilla.gnome.org/show_bug.cgi?id=722815

Also some code cleanup and passing all defined modifiers to
object methods.
cairo: use surface mime data to decrease file size for PDF and SVG

Assuming that the linked image file is already in the best possible
format/encoding to be used rather than recompressing. If the image
in the PDF turns black, that's becuase of a bug in cairo and Dia
not providing the fallback uncompressed rendering.
[gtk-osx] don't enforce gtk-engine usage

the blue scroll bars are not an improvement IMO
group_props.py: don't create a table with 0 rows

in case of no properties to show
tests: make test-sizeof compile with gcc/clang

both their preprocessors choke on ##, which is not necessary for
the case at hand