[PATCH] Fix window behavior when default button is present

[KapiX]

Currently the window hijacks almost all Enter key combos. Add/RemoveShortcut don't work for Enter in apps.

Attached is a patch that limits captures combos to Enter without modifiers.

[axeld]

Looks good, thanks. There are two minor style issues, though, that I would appreciate if you could fix them:

• constants should get the 'k' prefix. The name should then probably be improved to kAnyModifier.
• We prefer == 0 instead of !:

(modifiers() & modifierKeys) == 0

[axeld]

Looks great now, thank you!

[axeld]

Applied in hrev51292, thanks!