[PATCH] Fix build warnings on Windows, if building without OpenSSL

Hi,

the following patch was suggested by philipm on IRC. I've tested it and
it resolved the problem I had when building trunk:
"Warning: Using undeclared dependency '$(SVN_OPENSSL_LIBS'."

[[[
Following up on r1504208, add openSSL to the list of optional libraries to
properly surpress gen-make warnings on Windows when generating the project
files without openSSL support.
(patch suggested by philipm)

* build/generator/gen_win_dependencies.py
   (): Add openssl to _optional_libraries array.
]]]

I assume the patch should also be considered for backporting to 1.9
(same issue present there).
I didn't test 1.8 or 1.7 but looking at the code suggests it's not an
issue there since the patch which promoted openssl to a proper
dependency library was added post 1.8.

Regards,
Stefan