bug#21026: --exclude-dir matches search dir

[Aron Griffis]

This generates output:

$ grep -rl --exclude-dir=usr LINUX /usr/include

and this doesn't:

$ grep -rl --exclude-dir='usr*' LINUX /usr/include

This feels like a bug. My actual use-case is more like the following, but
the above seems like a more universal test case.

$ grep -rl --exclude-dir='.*' /home/aron/.virtualenvs/pp/src PATT

This surprised me by not generating any results. I had expected the
exclusion to only affect dirs within the given path, not match on the path
itself, but it seems to be aborting because '.*' matches '.virtualenvs'.
Is this a bug or just a bad assumption on my part?

$ grep --version
/usr/bin/grep (GNU grep) 2.21

Thanks,
Aron