Add a preference that can disable the fake SYSV SHM shim
https://bugs.webkit.org/show_bug.cgi?id=116127
<rdar://problem/13810524>

Patch by Simon Cooper <scooper@apple.com> on 2013-05-14
Reviewed by Alexey Proskuryakov.

* PluginProcess/mac/PluginProcessShim.mm:
(WebKit::shim_disabled):
(WebKit::shim_shmdt):
(WebKit::shim_shmat):
(WebKit::shim_shmget):
(WebKit::shim_shmctl):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150094 268f45cc-cd09-0410-ab3c-d52691b4dbfc