RELEASE 2.17.1: CMake-3 fix

Addresses: #450

This release should fix cases on some OS's and CMake-3.x versions, where either a build fail occurred, or an installation quietly skipped files.

Please be aware: This fix will cause 'empty' packages (those with no files to install) to fail during the build, with the message:

make: *** No rule to make target 'install'.  Stop.

The fix is to use the new build_command package attribute, to specify that your package doesn't have anything that needs building. Add this to your package.py:

build_command = False