Permitting the import command to accept a --user option.
The prose section of the help text for the command already said that -u and -m
are accepted, but -u was not listed in the table of options, and did not work.
Useful when accepting patches from other people made by hg diff rather than hg
export. For completeness, also accepting -d DATE.
[CHANGES: rebased against
d8878742a924, --no-commit option.]