[PATCH] Resolve testsuite interruption in SVN 1.8

Hi,

the attached patch is the outcome of talking with jcorval on IRC about a
test suite issue on Windows (release builds) in SVN 1.8. It resolves the
fact that the tests will be interrupted on Windows by a Windows popup
upon an abort()-call.

Atm this is triggered for the 1.8 test suite for the move-test (no 8)
which is marked as XFail and triggers an SVN_ERR_ASSERT() and therefore
breaks fully automated tests.

The chosen solution is based on an old discussion in 2011 which
triggered the case in a different (older) test:
http://svn.haxx.se/dev/archive-2011-01/0328.shtml
http://svn.haxx.se/dev/archive-2011-02/0011.shtml

The proposed patch introduces a new environment variable
(SVN_CMDLINE_DISABLE_WATSON_ON_ABORT) and if set, disables the Windows'
Watson crash reporting upon an abort-call.

More details available here: http://www.luke1410.de:8090/browse/MAXSVN-66

The patch was checked against trunk and 1.8.16 (running the whole test
suite (Win10 (1511) 64-bit x ra_local x fsfs)).

[[[
Resolve testsuite interruption on Windows in release mode, if a test
triggers
an abort.

* subversion/libsvn_subr/cmdline.c
  (svn_cmdline_init): check against the new
SVN_CMDLINE_DISABLE_WATSON_ON_ABORT
                      environment variable and disable Watson crash dumps in
                      this case

* subversion/tests/svn_test_main.c
  (svn_test_main): the same

* win-tests.py
  (): define the SVN_CMDLINE_DISABLE_WATSON_ON_ABORT environment
variable when
      running the test suite
]]]

Regards,
Stefan