commit: note when files are missing
Before, you could experience the following strange interaction:
$ hg commit
nothing changed
$ hg merge
abort: outstanding uncommitted changes
which confused at least one user in #mercurial.
hg debuginstall
$ hg debuginstall
Checking encoding (ascii)...
Checking installed modules (*/mercurial)... (glob)
Checking templates...
Checking commit editor...
Checking username...
No problems detected
hg debuginstall with no username
$ HGUSER= hg debuginstall
Checking encoding (ascii)...
Checking installed modules (*/mercurial)... (glob)
Checking templates...
Checking commit editor...
Checking username...
no username supplied (see "hg help config")
(specify a username in your configuration file)
1 problems detected, please check your install!
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