Add revlog.strip to truncate away revisions.
This updates the revlog data structures for index and nodemap in place
so the .d and .i files don't need to be reread after stripping away a revision.
#!/bin/sh
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "0 0"
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "0 0"
hg update 0
echo This is file c1 > c
hg add c
hg commit -m "commit #2" -d "0 0"
hg update -m 1
rm b
echo This is file c22 > c
hg commit -m "commit #3" -d "0 0"