Add nmodl python lib to PYTHONPATH of nrnivmodl_core_makefile (#317)

* Add the path to the nmodl python lib to the PYTHONPATH of nrnivmodl-core
* Fix PYTHONPATH to point to the correct dir in build

Author: iomaganaris

CMakeLists.txt

@@ -203,7 +203,8 @@ if(CORENRN_ENABLE_NMODL)
     set(CORENRN_NMODL_BINARY ${CMAKE_BINARY_DIR}/bin/nmodl${CMAKE_EXECUTABLE_SUFFIX})
     set(CORENRN_NMODL_INCLUDE ${CMAKE_BINARY_DIR}/include)
     set(ENV{PYTHONPATH} "$ENV{PYTHONPATH}")
-    set(CORENRN_NMODL_PYTHONPATH $ENV{PYTHONPATH})
+    set(nmodl_PYTHONPATH "${CMAKE_BINARY_DIR}/lib/python")
+    set(CORENRN_NMODL_PYTHONPATH "${nmodl_PYTHONPATH}:$ENV{PYTHONPATH}")
   endif()
   include_directories(${CORENRN_NMODL_INCLUDE})
   # set correct arguments for nmodl for cpu/gpu target