Blender was not configured to exit with non-zero return code on Python errors.
A bunch of tests worked around this but not all. This removes the need for such
workarounds.
Patch from Habib Gahbiche (zazizizou) moves the "run operator and
compare mesh to a golden" paradigm used in bevel and boolean tests
into a general framework that separates the test specs from the
blend files. Then adds some other operator and modifier tests using
the new framework. Diff D5357.id20724.diff was applied.
New .blend files, modifiers.blend and operators.blend are needed
in the tests/modeling svn directory; those were separately committed.
