this is possibly an upstream cmake issue, but in affects in particular users of a brewed python. I'm on Mavericks and have brewed python 2.7.6 and brewed cmake 2.8.12 ...
It's possible the work in #6 will fix the issue, but I don't know why FindPythonLibs would fail to find python when python3-dev is installed. Does a minimal CMake project have the same issue?