Ignore an xsnap build output

[erights]

After doing the normal installing building and testing, a git status was bugging me about an untracked fixture-snap-pool. It seemed harmless, so I am optimistically adding it to the closest .gitignore. With that, git status is clean again.

[dckc]

yes, this should be ignored. It's generated during snapshot testing (from 865ba54 )

But before I approve... is there some other filename convention I should have used, @warner ?

[warner]

Ideally it'd be a proper tempfile (mktmp or whatever), deleted when the test is complete. Failing that, it'd be nice to make it obviously not code, so maybe make a directory named _test_output/ and put it in there or something. But if that's too much of a hassle, I'm ok with just .gitignoreing the file as-is.

[dckc]

#2897 represents @warner 's suggestion to use temp files.

meanwhile, this is ok.