operations: Fix memory leak in photocopy.
operations: Fix spacing in photocopy.
Improve command line and env parsing

It is now possible to set application default values
before calling gegl_init(). These can be overridden
by environment variables, which are overridden by
command line arguments.
Remove -ftree-vectorize when building with clang
poly2tri-c: fix compiler warnings
buffer: fix warning about unused return value

Failing to resize the file is unrecoverable, so GEGL will probably
crash shortly after it happens. But now it will theoretically print
out why it's about to crash and GCC will stop complaining.
tests: don't use text in change-processor-rect

The output depends on the installed fonts and
can cause unwarranted failures.
Operations: Add OpenCL support to dot