added BLI_convertstringcwd, used so command line blendfiles and python scripts can be relative to the current path.

- was alredy doing this for blendfiles, but better to have in its own function.

header_text.c - renamed PATH_MAX, was defined by system includes.

source/blender/python/BPY_extern.h

@@ -94,7 +94,7 @@ extern "C" {
 	int BPY_menu_do_python( short menutype, int event );
 	int BPY_menu_do_shortcut( short menutype, unsigned short key, unsigned short modifiers );
 	int BPY_menu_invoke( struct BPyMenu *pym, short menutype );
-	void BPY_run_python_script( char *filename );
+	void BPY_run_python_script( const char *filename );
 	int BPY_run_script(struct Script *script);
 	void BPY_free_compiled_text( struct Text *text );