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.
pager.pager=p0 # $TESTTMP/sysrc:4
ui.editor=e1 # $TESTTMP/userrc:2
pager.pager=p2 # $PAGER
ui.editor=e1 # $TESTTMP/userrc:2