brush masks: allow one-click strokes

brush strokes always need a minimum of two nodes. in the one-click case we add a
helper node at very close distance.
Merge branch 'master' of github.com:darktable-org/darktable
Remove BOM byte from src/develop/masks/brush.c

This pleases GCC 4.2.
Merge branch 'master' of github.com:darktable-org/darktable
[l10] Swedish update of strings related to brush masks and the new
color balance module.
brush masks: minor improvements
Merge branch 'master' of github.com:darktable-org/darktable
Activate masks on the exposure module.
Merge pull request #277 from darktable-org/exposure-masks

Activate masks on the exposure module.
Activate multi-instance support for the exposure module.
Merge branch 'master' of github.com:darktable-org/darktable
Merge pull request #278 from darktable-org/exposure-multi-instance

Activate multi-instance support for the exposure module.
Merge branch 'master' of github.com:darktable-org/darktable