BUG/MINOR: config: fix typo in condition when propagating process binding

propagate_processes() has a typo in a condition :

	if (!from->cap & PR_CAP_FE)
		return;

The return is never taken because each proxy has at least one capability
so !from->cap always evaluates to zero. Most of the time the caller already
checks that <from> is a frontend. In the cases where it's not tested
(use_backend, reqsetbe), the rules have been checked for the context to
be a frontend as well, so in the end it had no nasty side effect.

This should be backported to 1.5.
BUG/MEDIUM: config: do not propagate processes between stopped processes

Immo Goltz reported a case of segfault while parsing the config where
we try to propagate processes across stopped frontends (those with a
"disabled" statement). The fix is trivial. The workaround consists in
commenting out these frontends, although not always easy.

This fix must be backported to 1.5.