[PATCH] Do not ignore --bin parameter for svnrdump when running Python tests

Hi,

I've noticed a small discrepancy: around trunk_at_r1547889, the core of the test
suite (subversion/tests/cmdline/svntest/main.py) always ignores the --bin
option for the svnrdump binary.

So, if you make a fresh checkout and try to run svnrdump_tests.py against the
installed version of Subversion, the test runner will complain about the
missing svnrdump binary:
[[[
  ./svnrdump_tests.py --bin=/usr/bin

  ... (in run_svnrdump)
  OSError: [Errno 2] No such file or directory
  FAIL: svnrdump_tests.py 1: dump: standard sbox repos
]]]

I've attached a patch to fix this issue. AFAIK [1], SVNKit does not include
the "j" version of svnrdump, so I did not touch the part of the setup that
handles the --use-jsvn option. Log message:
[[[
Do not ignore --bin parameter for svnrdump when running Python tests.

* subversion/tests/cmdline/svntest/main.py
  (svnrdump_binary): Update obsolete comment.
  (execute_tests): Override default svnrdump path when --bin option is set.

Patch by: Evgeny Kotkov <evgeny.kotkov{_AT_}visualsvn.com>
]]]

[1] http://svn.svnkit.com/repos/svnkit/trunk/svnkit-cli/build.gradle

Thanks and regards,
Evgeny Kotkov