The parallel_distribute() family of functions has been migrated to
GEGL. Remove the gimp_parallel_distribute() functions from
gimp-parallel, and replace all uses of these functions with the
corresponding gegl_parallel_distrubte() functions.
The next commit is going to parallelize gimpbrush-transform using
the gimp_parallel_distribute_foo() functions. To spare us a lot of
boilerplate code, we're going to use C++ lambdas as callback
arguments to these functions.
This commit does the initial conversion of gimpbrush-transform.c to
C++, renaming it to gimpbrush-transform.cc. We do this in a
separate commit, so that the changes are small enough for git to
register this as a renamed file, rather than a new file, so that we
don't lose the file's history.
