vignette: clip inner, unvignetted part of image (fixes #10041)

without this fix the inner area of the image preserves potentially unbounded values
while the vignette area is clipped. unter certain circumstances this leads to
visible artifacts at the transition (see redmine ticket). legacy history stacks
are handled as before. to take advantage of this fix you need to reset the
vignette module.
Hack around a spurious EOF comparison
Comment out an unused constant (clang complains)
Remove some dead code that clang caught
Merge pull request #647 from pedrocr/crw-warning-fix

Hack around a spurious EOF comparison in rawspeed
Merge pull request #648 from pedrocr/fix-clang-warnings

Fix clang warnings in rawspeed code