Prepend to full PYTHONPATH

[akorgor]

No description provided.

[terhorstd]

During the review please check if the module file glob works with both module systems, i.e. on the TCL-based legacy environment-modules, and on HPC (usually using the Lua lmod).

[jhnnsnk]

@terhorstd Please reassign this PR to @JanVogelsang as a reviewer.

[JanVogelsang]

Shouldn't the NEST_MODULE_PATH be determined in the same way?

setenv          NEST_MODULE_PATH        \$INSTALLDIR/lib64/nest

-->

setenv          NEST_MODULE_PATH        [glob -directory \$INSTALLDIR/ -type d lib*/nest/]

[JanVogelsang]

This one can be closed in favor of #61

[terhorstd]

Thanks, @JanVogelsang !