Add brew’s keg-only openssl to the search paths.
Attempt to link with the brewed libssl/libcrypto.
Use the correct search path for brewed openssl.
Don’t change search paths.
Don’t include the old dylibs.
Symlinks to brewed libcrypto.a & libssl.a.

When these symlinks are unable to be resolved, the linker just skips
past them on to the next entry in the search paths. Thus, this should
work fine for system dylibs (since the search path entries that would
resolve to brewed dylibs have been removed) and for brewed archives.
Merge pull request #356 from libgit2/fix-linking-against-new-libssh2-formula

Fix linking against new libssh2 formula