Add PeepholeMinimizeConditions pass.

This is split from the condition minimization logic in
PeepholeSubstituteAlternateSyntax.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=46298141
Import jQuery prop() patch.

Fixes issue 987.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=46303568
Do not count leading NOT in EXPR_RESULT.

Ignore the leading NOT in EXPR_RESULTs in PeepholeMinimizeConditions, as
it will be optimized away by PeepholeRemoveDeadCode.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=46305466