weak normalization
Weak normalization for secp256k1_fe_equal
Add _fe_normalizes_to_zero method
Add _normalizes_to_zero_var variant
Merge pull request #154

49ee0db Add _normalizes_to_zero_var variant (Peter Dettman)
eed599d Add _fe_normalizes_to_zero method (Peter Dettman)
d7174ed Weak normalization for secp256k1_fe_equal (Pieter Wuille)
0295f0a weak normalization (Pieter Wuille)