Potential bug in --color-words output

[Simeon Krastnikov <skrastnikov@gmail.com>]

Hello,

Given an initial file with the contents "not to be", which I then change 
to "to be", the output of 'git diff --color-words', is

   notto be

with the first three letters colored red. To me this seems incorrect as 
it implies, or at least misleadingly suggests, that there was no space 
between "not" and "to" in the original file. (Even though in that case 
the output is actually "nottoto be" with the "notto" in red and "to" in 
green.)

If instead I start with a file with contents "to be", which I then 
change to "not to be", then the output is as expected:

   not to be

(First three letters colored green.)

Am I correct in seeing this as a bug? If so, any tips on what parts of 
diff.c to look at when starting a patch?

Thanks,

Simeon