When consumeSemicolon fails to find a semicolon, don't consume anything.

When a Statement is not terminated by a semicolon, the consumeSemicolon
function terminates the range/loc of the node at the beginning of the next
node, including any whitespace or comments trailing after the Statement
node. Instead, it should revert back to the end of the previous node.

If you look carefully at the test changes included in this commit (all of
which I made by hand), I think you'll agree they make a lot of sense. The
only ones I'm not sure about are the end-of-Program positions: for
instance, the Program location for '\n42\n\n' now only includes the 42,
and not any of the whitespace. This was already true for the starting
position, but now it is also true for the ending position.

This inclusion of trailing comments/whitespace by consumeSemicolon has
been a very long-standing issue that I dealt with in
https://github.com/benjamn/recast using the
[LocationFixer](https://github.com/benjamn/recast/blob/6feb25024c6883bcfa027b95d3b5fa476ac179e9/lib/parser.js#L72-L101)
class (first introduced in September 2012), but I want to stop using that
class for performance reasons, and I've come to realize I can't correctly
fix all cases anyway (I can rewind over whitespace, but not so easily over
comments, without implementing something like unskipComment), so I believe
this logic is better implemented in esprima.js.

https://code.google.com/p/esprima/issues/detail?id=574