Avoid CMP0048 warning

[jagerman]

Fixes #567.

If pybind's CMakeLists gets loaded via an include_directory from another CMakeLists with a higher minimum version (e.g. 3.0), the project() command without a version produces a CMP0048 warning.

This commit explicitly requests the old behaviour (if the policy exists in the active cmake).

[dean0x7d]

Setting a policy to OLD is only meant to be a temporary workaround. The OLD policies are deprecated and future versions of CMake are free to remove them. At that point the old behavior becomes an error.

In this case, it should be possible to set the policy to NEW without any other changes. project() sets the version variables to false first and the manual assignment happens later. It would only be a problem if the order was reversed.

[jagerman]

Changed it to NEW.

[wjakob]

There is a strange failure on Travis-OSX for Python 3.5 (likely unrelated to this PR). Is it possible that gfortran needs to be installed on this platform?

[dean0x7d]

Homebrew just got Python 3.6 (brew install python3), but numpy and scipy don't have binary wheels for 3.6 yet so it's trying to compile from source and failing. Probably best to allow the failure temporarily until the wheels are released.

[wjakob]

ok, sounds good to me. @jagerman -- do you want to include a line in .travis.yml to allow the test failure?

Thanks and happy Christmas
-Wenzel

[wjakob]

Merged, thanks!