Removes nprocs variable, counts processes
Fixes bug if new processes resumes first

When we fork/clone, the new process might start its execution first (and
tracer sees it get a SIGTRAP). In this case, we wait for the fork call
to return before we insert things into the database and resume it
(previously, a unknown process would be created for it, plus a duplicate
when fork actually returned. That was bad).
Merge branch 'master' into 'fork-race-condition'

Conflicts:
	reprozip/native/tracer.c
Prints number of processes (and unknown processes)
Merge branch 'fork-race-condition' into 'master'

Conflicts:
	reprozip/native/tracer.c