Missing CMake configuration file

[afossa]

The file PagmoPNFFindBoost.cmake was removed with the last commit to master.
Although the plugin is built correctly and the tests pass, this file is still required when configuring a project that depends on pagmo_plugins_nonfree with CMake.
Manually picking this file from 15f0eb1 and copying it into CMAKE_INSTALL_PREFIX/lib/cmake/pagmo_plugins_nonfree/ solves the issue.

[darioizzo]

I believe that is indeed a bug as the file is not needed, but its still looked for in the cmake.in ... I will fix this in next release, in the meantime your workaround seems to make sense.