Fixes issue1336 - a race condition could occur when forking if the gc kicked in during the critical section.  solution: disable gc during that section.  Patch contributed by jpa and updated by me to cover the race condition still existing what therve from twistedmatrix pointed out (already seen and fixed in twisted's own subprocess code).
Fixes issue1336 - a race condition could occur when forking if the gc
kicked in during the critical section.  solution: disable gc during
that section.  Patch contributed by jpa and updated by me to cover the
race condition still existing what therve from twistedmatrix pointed
out (already seen and fixed in twisted's own subprocess code).

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator