3693: combsimp adjustment for ratios
fix failing tests (confirmed equivalence numerically)
allow for iteration in rule_gamma
ExpBase.as_numer_denom synched with Pow

With this change, we no longer need to look for 1/(g-1) in numer nor
1/g in denom.
Merge branch 'comb' of github.com:smichr/sympy into comb

Conflicts:
	sympy/simplify/simplify.py
make expand run in parallel