Issue #81: Revert "Issue #42: removed hard-coded Python version strin…

…g from CMake config"

as it causes problems on Linux

This reverts commit f11190a.

src/cmake/pythonlibs/CMakeLists.txt

@@ -1,12 +1,9 @@
 CMAKE_MINIMUM_REQUIRED(VERSION 3.2.0)
 
-FIND_PACKAGE(PythonLibs REQUIRED)
+FIND_PACKAGE(PythonLibs 2.7 REQUIRED)
 SET(PYTHON_INCLUDE_DIRS ${PYTHON_INCLUDE_DIRS}
     CACHE INTERNAL "PythonLibs include dirs"
 )
 SET(PYTHON_LIBRARIES ${PYTHON_LIBRARIES}
     CACHE INTERNAL "PythonLibs libraries"
 )
-SET(PYTHONLIBS_VERSION_STRING ${PYTHONLIBS_VERSION_STRING}
-    CACHE INTERNAL "PythonLibs version string"
-)