Failure on "x86 Ubuntu Shared 3.x" at revision af388201c9976aebc4a8a433c95bfc4a1abe014b.

I added an assertion in tracemalloc_init() to ensure that the reeentrant flag is set at the end of the function.

The reentrant flag was no more set at tracemalloc_start() entry for an unknown reason.

http://buildbot.python.org/all/builders/x86%20Ubuntu%20Shared%203.x/builds/12905/steps/test/logs/stdio
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0:08:50 [183/400] test_tracemalloc
[pid 14926, tid 1437466048] tracemalloc_start()
[pid 14926, tid 1437466048] tracemalloc_init()
[pid 14926, tid 1437466048] tracemalloc_init(): exit (already initialized)
python: ./Modules/_tracemalloc.c:1058: tracemalloc_start: Assertion `get_reentrant()' failed.
Fatal Python error: Aborted

Current thread 0x55adfdc0 (most recent call first):
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/test_tracemalloc.py", line 97 in setUp
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/case.py", line 596 in run
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/case.py", line 648 in __call__
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/suite.py", line 122 in run
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/suite.py", line 84 in __call__
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/suite.py", line 122 in run
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/suite.py", line 84 in __call__
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/unittest/runner.py", line 176 in run
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/support/__init__.py", line 1802 in _run_suite
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/support/__init__.py", line 1836 in run_unittest
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/test_tracemalloc.py", line 999 in test_main
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/libregrtest/runtest.py", line 162 in runtest_inner
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/libregrtest/runtest.py", line 115 in runtest
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/libregrtest/main.py", line 306 in run_tests_sequential
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/libregrtest/main.py", line 367 in run_tests
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/libregrtest/main.py", line 405 in main
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/libregrtest/main.py", line 446 in main
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/libregrtest/main.py", line 468 in main_in_temp_cwd
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/test/__main__.py", line 3 in <module>
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/runpy.py", line 85 in _run_code
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/runpy.py", line 184 in _run_module_as_main
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