Ignore unrecognized fields when comparing AST nodes

This would help work around the problem identified here: https://github.com/benjamn/recast/issues/89#issuecomment-45261490

This is the line that probably needs to change to use `types.eachField`: https://github.com/benjamn/recast/blob/547947e20036a18a46ea140680f866772872070d/lib/patcher.js#L292

Start at lib/patcher.js around line 292, then inspect the issue 89 comment and the available types.eachField helper. Confirm how AST nodes are currently compared and verify that the issue 89 scenario succeeds once unrecognized fields are ignored.

Written by the indexing model from the issue text.