add a .gitignore

and hide the files made by the build system
Merge remote-tracking branch 'origin/master'

Conflicts:
	.gitignore
Merge remote-tracking branch 'upstream/master'
some fixups to image display

- disable the backing pixmap and double-buffering, we get a better
  result doing this ourselves

- fix up vips reference counting within imagearea

- use the vips_sink_screen() mask image to suppress painting of
  uncalculated pixels

  this fixes the nasty black "flash" we used to get when a toggle on the
  right was changed

- remove the invalidate stuff again, vips-7.39+ does not need this

  unless you use git master vips you'll see black pixels

  add a couple of vips_image_invalidate_all() calls for earlier vipses
Merge pull request #2 from jcupitt/display-patch-2

Display patch 2