tests/testlib/common.sh

revlog: make _partialmatch fail fast on almost-hex inputs

Before this change, resolving a revision like [0123456789^] on
a large repo can take multiple seconds because:

- hg does not realize this is a revset, so it tries various things,
including _partialmatch(b"0123456789^")
- after the rust lookup fails, it falls back to pure hg
- pure hg takes all-but-last chars and converts them to binary,
which *succeeds*, so it does the expensive part.

mkcommit() {
   name="$1"
   shift
   echo "$name" > "$name"
   hg add "$name"
   hg ci -m "$name" "$@"
}