Support grep's "-w" flag [PATCH] about codesearch HOT 3 OPEN

Blindly adding \b to the start and end of the pattern fails for cases where the 
pattern _already_ starts or ends on a word-boundary.

I've updated the patch with a better fix.  I've copied the implementation of 
regex.isWordByte() because we need to know what regex thinks is a word 
boundary.  An alternate fix would be to export this function directly from the 
package.

This patch only works for trivial cases, and making it work in the full case is 
Hard(er).

Full discussion on the patch set:

https://codereview.appspot.com/6162045/

I'm leaving this open for now, because it's still a nice feature.