patch-python_geographiclib_CMakeLists.txt

--- python/geographiclib/CMakeLists.txt.orig	2017-10-05 10:11:24 UTC
+++ python/geographiclib/CMakeLists.txt
@@ -4,9 +4,10 @@
 file (GLOB PYTHON_FILES [A-Za-z_]*.py)
 file (GLOB TEST_FILES test/[A-Za-z_]*.py)
 if (COMMON_INSTALL_PATH)
-  set (INSTALL_PYTHON_DIR "lib${LIB_SUFFIX}/python/site-packages")
+  set (INSTALL_PYTHON_DIR "lib${LIB_SUFFIX}/python/site-packages"
+    CACHE STRING "")
 else ()
-  set (INSTALL_PYTHON_DIR "python")
+  set (INSTALL_PYTHON_DIR "python" CACHE STRING "")
 endif ()
 
 install (FILES ${PYTHON_FILES}