tests: convert the 'file://\$TESTTMP' rule to an automatic substitution
The rule only triggered on non Windows platforms, even though Windows also
required an adjustment. Automatic seems better.
The aggressive globbing in test-subrepo-svn.t was found and rewritten by the
substitution.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.