Fix #34954, due to hardcoded key release it was impossible to change key
for sample color and exit the operator. Also tweaked stencil to behave
similarly, so it is now possible to assign custom keys to stencil
control.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55967 954f8c5b-7b00-dc11-b283-0030488c597c
Fix issue with bright frames appearing in clip editor when compositor is open.

Allocate float buffer outside of image buffer,
so work-in-progress color space conversion doesn't
interfere with other parts of blender.

Covers most of cases -- since image buffer wouldn't
have partially-update float buffer all the rest
areas would be happy.

However, if there're places which updates float
buffer from byte buffer, it's still possible
some WIP color space conversion is displayed on
the screen.

But what a heck someone will do such a crappy
conversion anyway!

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55968 954f8c5b-7b00-dc11-b283-0030488c597c