OpenCL: Add possibility to override build options using environment
variable or john.conf.  Also add custom build options capability to
sha256crypt-opencl and sha512crypt-opencl, as a PoC. If given, they
will be concatenated with global options.
Add clReleaseProgram() to Sayantan's formats.
Add a --stress-test[=TIME] option that is just like --test except
it loops the test(s) forever.
Memory leak bugfixes to mscash2, bcrypt and lotus5 OpenCL formats.
Office2007-opencl: Use shared auto-tune.
Office2010-opencl: Use shared auto-tune.
Office2013-opencl: Use shared auto-tune.
encfs-opencl: Use shared auto tune.
krb5pa-sha1-opencl: Use shared auto tune.
krb5pa-md5-opencl: Use shared auto tune.
ntlmv2-opencl: Use shared auto tune.
mysql-sha1-opencl: Use shared auto tune.
Minor fixes for the last eight commits.
Allow 10s total for encfs-opencl. It's a lot of iterations!
Drop some unneeded code from raw-md4/5 OpenCL formats.
Drop obsoleted code from OpenCL formats, and fix a bunch of little
issues.
OpenCL: Ensure unmapping of buffers.
Fix generic build (-f Makefile.legacy) breakage
which was caused by commit 7ec88f81a3826006e667ff8b2972ec89d87612fa.
Fix to #739.
Ops: I missed one cast.