+ Add a max number of fails option to the resolved context so we can bailout of a resolve early.
Merge remote-tracking branch 'mark/solver_max_fails' into testing_1

Conflicts:
	src/rez/resolved_context.py
	src/rez/solver.py
-some updates to Mark's max-fails PR
-added --time-limit
-added 'callback' to ResolvedContext