git-grep: small suggestion, -w flag

Here's a stupid little git-grep suggestion.

I recently transitioned from the use of egrep to git-grep, and i 
like it very much (it nicely excludes build related files, 
etc.), but there's one small detail: the lack of the -w flag.

It's equivalent to this pattern:

   git grep '\<tick_length\>'

And it's the most common grep flag i (and i suspect many others) 
use, in addition to the (already supported) -l flag.

When grepping for symbols in a large repository (such as the 
Linux kernel) -w is very common and very useful - there's many 
similar symbols, variants of each other. I use it when seeing a 
symbol in an oops, etc.

While i realize that git-grep does not want to be a full grep 
replacement, there's a real usability difference between having 
to type:

   git grep '\<schedule\>'
   git grep -w schedule

(especially since backslash is a seldom used key during a normal 
workflow, so accessing it is often a small mental hickup.)

	Ingo