Fix boost_python discovery for distros with different naming scheme

[rrika]

The current method probes

boost_python_py351
boost_python_py35
boost_python_py3
boost_python

On Arch Linux however the name of the library is

boost_python3

So I added that to the cmakefile.

[nlgranger]

As far as I can tell, this is the same bug as #3345.

[rrika]

@pixelou you're right, your patch additionally checks for

boost_python351
boost_python35

though I don't know any distribution that names its libraries like that

[rarensu]

this merge would be pretty great since it's still an issue for some folks like me.