Memory stress test for UtfNormal issue re bug 28146

Memory stress test for UtfNormal issue re bug 28146

This pulls the source texts used for the UtfNormalBench.php benchmarks, repeats them into much larger strings, and attempts to reproduce an out-of-memory error in the middle of UtfNormal::cleanUp():

$ php
Testing testdata/washington.txt (English text)...
     quickIsNFCVerify 1078.3ms   14,969,652 bytes/s (changed)
              cleanUp  992.1ms   16,270,594 bytes/s (no change)
Testing testdata/berlin.txt (German text)...
PHP Fatal error:  Allowed memory size of 136314880 bytes exhausted (tried to allocate 71 bytes) in /var/www/trunk/includes/normal/UtfNormal.php on line 285

Exact failure point may require adjustment depending on platform, etc.