Cmake: General improvements:

Fix up rpath settings:

CMake is typically used for developer builds; and as such, we should
make an attempt to have our own libraries and tools _not_ pick up system
libraries, unless we are a system install. This mimics existing
autotools behavior.

Silence CMP0026 warning on Windows

This "old" behavior here is intended, because the `LOCATION` property
can give us the name of the install path before the project has been
generated, allowing us to transform their names into proper PDB paths to
include within the final distribution.

Add package name for VC12 (VS 2013)

We don't build these packages officially yet, but it still makes it
nicer.

Use homebrew OpenSSL if available
The default OS X OpenSSL spams us with deprecation warnings; we'd be
better off using Homebrew's version.

Change-Id: I99af9f8e9b94f77e8f16cba80481645a30564f12
Reviewed-on: http://review.couchbase.org/42443
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>