url: be stricter about detecting schemes
While the URL parser is very forgiving about what characters are
allowed in each component, it's useful to be strict about the scheme
so we don't accidentally interpret local paths with colons as URLs.
This restricts schemes to containing alphanumeric characters, dashes,
pluses, and dots (as specified in RFC 2396).
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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