set GRASS_PYTHON if it isn't (trac https://trac.osgeo.org/grass/ticket/534; merge from devbr6)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@40436 15284696-431f-4ddb-bdfa-cd5b030d7da7

mswindows/GRASS-Installer.nsi

@@ -569,8 +569,9 @@ Section "GRASS" SecGRASS
 	FileWrite $0 'rem Path to the proj files (notably the epsg projection list)$\r$\n'	
 	FileWrite $0 'set GRASS_PROJSHARE=%GRASSDIR%\proj$\r$\n'
 	FileWrite $0 '$\r$\n'
-	FileWrite $0 'rem Path to the python directory$\r$\n'	
+	FileWrite $0 'rem Path to the python directory$\r$\n'
 	FileWrite $0 'set PYTHONHOME=%GRASSDIR%\Python25$\r$\n'
+	FileWrite $0 'if "x%GRASS_PYTHON%" == "x" set GRASS_PYTHON=python\r$\n'
 	FileWrite $0 '$\r$\n'
 	FileWrite $0 'set WINGISBASE=%GRASSDIR%$\r$\n'
 	FileWrite $0 '"%WINGISBASE%\etc\Init.bat" %*'
@@ -670,6 +671,9 @@ Section "GRASS" SecGRASS
 	FileWrite $0 'export PYTHONPATH$\r$\n'
 	FileWrite $0 'PYTHONHOME="$INSTALL_DIR\Python25"$\r$\n'
 	FileWrite $0 'export PYTHONHOME$\r$\n'
+	FileWrite $0 'if [ -z "$$GRASS_PYTHON" ] ; then\r$\n'
+	FileWrite $0 '   GRASS_PYTHON=python; export GRASS_PYTHON\r$\n'
+	FileWrite $0 'fi\r$\n'
 	FileWrite $0 '$\r$\n'
 	FileWrite $0 '# Set the GRASS_PROJSHARE variable$\r$\n'
 	FileWrite $0 'GRASS_PROJSHARE="$INSTALL_DIR\proj"$\r$\n'