Fix escaping in YAML RegExp.

Fix escaping in YAML RegExp.

This was causing it to try to parse "m4" as a number, which fails.
Fixes #9128.
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=20107

[nweiz, 2013-03-15 18:14:21]

We should probably just use r""-style strings for all of these. I don't think
those were implemented when I first wrote the library (or maybe I just didn't
know about them).

[Bob Nystrom, 2013-03-15 18:19:22]

On 2013/03/15 18:14:21, nweiz wrote:
> We should probably just use r""-style strings for all of these. I don't think
> those were implemented when I first wrote the library (or maybe I just didn't
> know about them).

I figured this was the simplest change and was consistent with other patterns.
Also, I wasn't sure if "$" still needed to be escaped in raw strings. I can
change them all over if you really want.

[nweiz, 2013-03-15 18:22:25]

On 2013/03/15 18:19:22, Bob Nystrom wrote:
> On 2013/03/15 18:14:21, nweiz wrote:
> > We should probably just use r""-style strings for all of these. I don't
think
> > those were implemented when I first wrote the library (or maybe I just
didn't
> > know about them).
> 
> I figured this was the simplest change and was consistent with other patterns.
> Also, I wasn't sure if "$" still needed to be escaped in raw strings. I can
> change them all over if you really want.

It shouldn't be too hard to do so, right? And it'll be nicer long-term.

[Bob Nystrom, 2013-03-15 20:11:18]

Okey dokey. Updated everything to raw strings. PTAL!

[nweiz, 2013-03-15 20:26:43]

lgtm

[Bob Nystrom, 2013-03-15 20:48:36]

Committed patchset #2 manually as r20107 (presubmit successful).