convert: make contents of "extra" dict available from sources, for sinks.
This breaks hash preservation for hg->hg conversion, as each converted
change gets a convert_revision item added to its extra dict. Ugh.
#!/bin/sh
cat > $HGRCPATH <<EOF
[extensions]
alias=
[alias]
myinit = init
cleanstatus = status -c
unknown = bargle
ambiguous = s
recursive = recursive
EOF
echo '% basic'
hg myinit alias
echo '% unknown'
hg unknown
echo '% ambiguous'
hg ambiguous
echo '% recursive'
hg recursive
cd alias
echo foo > foo
hg ci -Amfoo
echo '% with opts'
hg cleanst