Made all header files to have LABWC_ prefix in include guard identifers.
Converted from __LABWC_ in 35 include/ files.
Converted from __LAB_ in 5 include/ files.
Added LABWC prefix to 3 include/ files.
Added include guards to 3 include/ files.
The double underscores were removed since according to C standard
those "are always reserved for any use".
When wanting to snap to a region when starting the move
operation with A-Left (or a similar mousebind which includes a
modifier), the modifier - or another one - must be pressed again.
Fixes#761
