* tests: fix add.sh that created repos directly in /tmp
Doesn't actually fix of add.sh (only a slight improvement in the script)
but does fix apply.sh that wrongfully had an extra "cd .." .
* tests/network: bake process id into REMOTE_DIR
* allow shell tests to run in parallel when using --myers and --patience
It allows running them in parallel by putting the diff algorithm name
into the temp directories; OK.
* allow running the diff.sh test in parallel
* make spurious failures of hashed storage tests less likely
It uses Darcs.Util.Lock.withTempDir to do so, which is also a code