builddependencies: don't add dependency on revision outside input set
This was already handled in the single-successor case, but had been
missed in the multiple-successors case.
Note that there seems to be a copy of builddependencies() in the
topics extension. I don't use topics more than I have to, so I'll let
someone else fix that code.
#require test-repo pyflakes
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)
$ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
> | xargs pyflakes 2>/dev/null