Optimize the heal tool

Adjust over-relaxation factor as a function of problem size.
Remove the second array, and update in-place.
Factor branches and indexing out of the inner loop, instead precompute a list
of pixels inside the brush mask and what neighbors they have.
Switch from scalar double to simd float.

Speedup (of the laplace part, excluding gamma correction): 10x-20x, depending on brush size.
app: fix saving/loading of .xcf.gz and other compressed XCFs

Make file_utils_uri_get_ext() public and use it instead of
strrchr(uri, '.'). Also add "xz" to the list of matched special cases,
and some cleanup.
app: Remove an unused variable and associated dead code.
Revert "Optimize the heal tool"

This reverts commit d7066a1e2fef00a3f80aac77ab3c366713f0ef52
because I pushed it accidentially, it still needs some cleanup.
app: fix file magic matching

file_procedure_find(): check all procedures' magics and not the first
precedure's magics #procedures times, sigh.
Optimize the heal tool

Adjust over-relaxation factor as a function of problem size.
Remove the second array, and update in-place.
Factor branches and indexing out of the inner loop, instead precompute a list
of pixels inside the brush mask and what neighbors they have.
Switch from scalar double to simd float.

Speedup (of the laplace part, excluding gamma correction): 10x-20x, depending on brush size.
app: fix saving/loading of .xcf.gz and other compressed XCFs

Make file_utils_uri_get_ext() public and use it instead of
strrchr(uri, '.'). Also add "xz" to the list of matched special cases,
and some cleanup.
app: Remove an unused variable and associated dead code.
Revert "Optimize the heal tool"

This reverts commit d7066a1e2fef00a3f80aac77ab3c366713f0ef52
because I pushed it accidentially, it still needs some cleanup.
app: fix file magic matching

file_procedure_find(): check all procedures' magics and not the first
precedure's magics #procedures times, sigh.
app: foreground select tool add call for gegl op but need patch in gegl too for return mask from matting-global
Merge remote-tracking branch 'upstream/master'