convert: allow the converter_source to say "skip this revision"
If getchanges returns a string, it's assumed to be the id of an
already converted revision. We map the current revision to the same
revision this converted revision was mapped to.
To allow skipping a root revision, getchanges can return the special
string 'hg-convert-skipped-revision' (a.k.a. common.SKIPREV), which
hopefully won't clash with any real id.
The converter_source is responsible for rewriting the parents of the
commit objects to make sure the revision graph makes sense.
#!/bin/sh
mkdir t
cd t
hg init
echo 1 > a
hg ci -qAm "first" -d "1000000 0"
hg cp a b
hg mv a c
echo 2 >> b
echo 2 >> c
hg ci -qAm "second" -d "1000000 0"
hg co -C 0
echo 0 > a
echo 1 >> a
hg ci -qAm "other" -d "1000000 0"
hg merge --debug
echo "-- b --"
cat b
echo "-- c --"
cat c