Make TcLevel increase by 1 not 2
Make TcLevel increase by 1 not 2

Make the TcLevel of a flatten-meta-var be always zero.
See TcType.fmvTcLevel.

This allows the levels of implication constraints to to
up by 1 each time instead of 2, which is less confusing.

This change has no effect on type checking.

sdiehl/ghc,shlevy/ghc,mettekou/ghc,olsner/ghc,sdiehl/ghc,mettekou/ghc,shlevy/ghc,ezyang/ghc,mettekou/ghc,mettekou/ghc,mettekou/ghc,olsner/ghc,sdiehl/ghc,olsner/ghc,ezyang/ghc,shlevy/ghc,sdiehl/ghc,sdiehl/ghc,ezyang/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,mettekou/ghc,ezyang/ghc,olsner/ghc,sdiehl/ghc,olsner/ghc,shlevy/ghc,ezyang/ghc,olsner/ghc,shlevy/ghc,mettekou/ghc,sdiehl/ghc,olsner/ghc