merge noise in git-shortlog output

Looking at the shortlog information for 2.6.13 there are a lot (eleven)
of changes attributed to me that look like:

  Auto merge with /home/aegl/GIT/linus

This is valid (I really did make all those commits, they happen every
time I merge the "linus" branch into my release branch, which I like to
do quite often so I'm working near the bleeding edge), but it doesn't
seem all that useful in the "short" log output[1]

If "Auto merge" isn't a good string to match for the purposes of
trimming, then I can make my scripts use something else.

-Tony

[1] unless I can persuade Intel to base my bonus on the number of
commits I get included into the base :-)