Fix some test suite bugs related to clean-up.  These are mostly not causing problems in normal test runs, but one problem seen by Danial Shahaf is that since r1303316 some tests (e.g. export_tests 19,20) would fail if run without cleanup afterwards and then run again.  Another bug fixed here is that some paths were not being cleaned up.  Another potential bug fixed here is that it was possible for a test to start using a WC path that still existed from a previous test run if it didn't start by calling sbox.build().
Fix some test suite bugs related to clean-up.  These are mostly not causing
problems in normal test runs, but one problem seen by Danial Shahaf is that
since r1303316 some tests (e.g. export_tests 19,20) would fail if run
without cleanup afterwards and then run again.  Another bug fixed here is
that some paths were not being cleaned up.  Another potential bug fixed here
is that it was possible for a test to start using a WC path that still
existed from a previous test run if it didn't start by calling sbox.build().

Found by: danielsh
          me
(danielsh: the bug exposed by export_tests 19,20 after a no-cleanup run;
me: the others)

* subversion/tests/cmdline/svntest/sandbox.py
  (__init__): Initialize the list of paths to be cleaned up. Delete, create
    and remember a directory for temporary files here ...
  (get_tempname): ... instead of just creating it here if it didn't exist.
  (_set_name): Don't reset the list of paths to be cleaned up, so we don't
    lose any of them when we change the name of the sandbox.  Ensure any
    existing WC and repo directory is deleted.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion