Running MediaWiki PHPUnit Database tests with `docker-registry.wikimedia.org/releng/quibble-jessie-php55:0.0.8` ends up exiting due to a SIGSEGV:
```
php tests/phpunit/phpunit.php --debug-tests --group Database --exclude-group Broken,ParserFuzz,Stub
Using PHP 5.5.38-4+wmf1+jessie
<...>
................Traceback (most recent call last):
File "/usr/local/bin/quibble", line 9, in <module>
load_entry_point('quibble==0.0.0', 'console_scripts', 'quibble')()
File "/usr/local/lib/python3.4/dist-packages/quibble/cmd.py", line 402, in main
cmd.execute()
File "/usr/local/lib/python3.4/dist-packages/quibble/cmd.py", line 397, in execute
quibble.test.run_phpunit_database(mwdir=self.mw_install_path)
File "/usr/local/lib/python3.4/dist-packages/quibble/test.py", line 122, in run_phpunit_database
run_phpunit(*args, **kwargs)
File "/usr/local/lib/python3.4/dist-packages/quibble/test.py", line 117, in run_phpunit
subprocess.check_call(cmd, cwd=mwdir, env={'LANG': 'C.UTF-8'})
File "/usr/lib/python3.4/subprocess.py", line 561, in check_call
raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['php', 'tests/phpunit/phpunit.php', '--debug-tests', '--group', 'Database', '--exclude-group', 'Broken,ParserFuzz,Stub']' returned non-zero exit status -11
```
-11 is Python `subprocess.check_call()` setting a negative exit code https://bugs.python.org/issue27167 Signal 11 is SIGSEGV: `Invalid memory reference` / `segmentation fault` which produces a core dump.
A build with sqlite is not affected, and REL1_30 pass. So something introduced between REL1_30 and master causes the issue. Most probably in the MySQL php5.5 extension.