Turns out that git has a feature I didn't know about; it will expand
wildcards and other stuff in filenames passed to many git commands. This is
on top of the shell's expansion.

That led to some broken behavior by `git annex add 'foo.*'`
and, it could lead to other probably unwanted behavior, like `git annex
drop 'foo[barred]'` dropping a file named `food` in addition to
`foo[barred]`

For now, I've disabled this git feature throughout git-annex. If you relied
on it for something, let me know, I might think about adding it back in
specific places where it makes sense.

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Improved `git annex importfeed` to check the itemid of the feed and avoid
re-downloading a file with the same itemid. Before, it would add duplicate
files if a feed kept the itemid the same, but changed the url. This was
easier than expected because annex.genmetadata already caused the itemid
to be stored in the git-annex metadata. I just had to make it check the
itemid metadata, and set itemid even when annex.genmetadata isn't set.

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Also got 4 other bug reports fixed, even though I feel I'm taking it easy
today. It's good to be relaxed again!
