Fix variance unit conversion.

If all values are scaled by a constant, the variance is scaled by the
square of that constant.

https://code.google.com/p/esprima/issues/detail?id=397
Fix variance unit conversion.

This is also needed for browser-based benchmarks.

https://code.google.com/p/esprima/issues/detail?id=397
Fix \v being treated as v in IE < 9

IE < 9 treats '\v' as 'v' instead of a vertical tab ('\x0B').
Read more: http://mathiasbynens.be/notes/javascript-escapes

https://code.google.com/p/esprima/issues/detail?id=405
UnaryExpression should have prefix: true

https://code.google.com/p/esprima/issues/detail?id=418