F/ssl

Hi algernon!

Could you review my commits since the latest review/pull request? I have done a couple of things, including:
 * Code refactoring
 * Making OpenSSL a hard dependency again (as requested)
 * Fixing some memory leaks and other bugs
 * Implemented better data hiding for mongo_ssl_ctx
 * Added mongo_ssl_ctx unit test (setter/getter functions)

I believe that the tests call each new function now, but I would be happy to see a code coverage. Unfortunately, coverage.sh fails to do that on my machine, no matter which directory I am attempting to run it from. (It seems, that variables srcdir and builddir are not properly so it cannot find the corresponding library files for source files, so it skips all of them because the condition in line 17 is not met.)

Any suggestions, notes? Where to go next?

Thanks a lot!

sirius