run-tests: give each child its own tmp dir (issue1911)
Fixes bug introduced by f8b4df4b033d (issue1911: --tmpdir plus parallel
mode = fail), and also fixes the long-standing quirk that parallel mode
created multiple /tmp/hgtests.XXXXXX directories. Now there is only one
/tmp/hgtests.XXXXXX, with child0, child1, etc. under it.
#!/bin/sh
# test dirstate._dirs refcounting
hg init t
cd t
mkdir -p a/b/c/d
touch a/b/c/d/x
touch a/b/c/d/y
touch a/b/c/d/z
hg ci -Am m
hg mv a z