bash: function export hardening patch

Another day another bash version bump. This is the final version of the
patch to add a special prefix and suffix to exported functions in the
environment, preventing bugs similar to the previous two from becoming
remotely exploitable.

http://lists.gnu.org/archive/html/bug-bash/2014-09/msg00279.html

There still remain two less significant memory-access issues, dubbed
CVE-2014-7186 and CVE-2014-7187. So expect another bump soon.
http://www.openwall.com/lists/oss-security/2014/09/25/32
Merge pull request #889 from marineam/bash50

bash: function export hardening patch