Fix CMake Python configuration bug

[ahundt]

If multiple versions of python are installed, the current CMake scripts may not find the correct version of Python and may have version mismatches between the interpreter and python library.

Python remains optional with these changes.
A specific python version can now be selected by setting PYTHON_VERSION_PANGOLIN.
Python versions can vary by default unless EXACT_PYTHON_VERSION=ON
The python library version must now match the interpreter version exactly.
If all required python dependencies are found, pangolin python utilities are now enabled by default.
Changes incorporate the following BSD licensed cmake code:

https://github.com/BVLC/caffe/blob/32bf5c7ad804ad683aa5ea9382209e9284451e5f/CMakeScripts/FindNumPy.cmake
https://github.com/NikolausDemmel/CMake/pull/2/files
https://github.com/Kitware/CMake/blob/86578eccf2e82286248796bad1032cd0e3a5e1e2/Modules/SelectLibraryConfigurations.cmake

Based on my pull request for the same python cmake issues in pybullet:
bulletphysics/bullet3#1131
bulletphysics/bullet3#1107

[stevenlovegrove]

Thanks for this patch, though it is failing the CI on Linux. Looking at your changes, I can't say that I really understand why.

[ahundt]

Maybe one of the variable names was accidentally changed so something required isn't being linked?

Linking CXX executable VideoViewer
../../src/libpangolin.so: undefined reference to `forkpty'
../../src/libpangolin.so: undefined reference to `openpty'
collect2: error: ld returned 1 exit status
make[2]: *** [examples/HelloPangolin/HelloPangolin] Error 1
make[1]: *** [examples/HelloPangolin/CMakeFiles/HelloPangolin.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
../../src/libpangolin.so: undefined reference to `forkpty'
../../src/libpangolin.so: undefined reference to `openpty'

It is funny that mac and windows are where things are ok. I was hoping this would just be a helpful fix not a big debugging thing... hmm maybe it is flaky? will close and reopen

[ahundt]

should work now, second commit based on bulletphysics/bullet3#1331

[ahundt]

Its green 👍

[ahundt]

@stevenlovegrove bump

[stevenlovegrove]

I'm sorry I never got to merging this - I was put off by it's size and references to irrelevant things like numpy etc.

Much better python integration has recently been added to Pangolin via pybind11, including more robust CMake python handling - hopefully that solves your problem?

[ahundt]

no worries, I ended up sticking to v-rep in the end except for a utility I use occasionally that depends on pangolin. It seems nice overall! Thanks, closing.