Fix constness of msGetPath() argument

Author: rouault

mapserver.h

@@ -2228,7 +2228,7 @@ void msPopulateTextSymbolForLabelAndString(textSymbolObj *ts, labelObj *l, char
   MS_DLL_EXPORT void msReplaceChar(char *str, char old, char sznew);
   MS_DLL_EXPORT char *msCaseReplaceSubstring(char *str, const char *old, const char *sznew);
   MS_DLL_EXPORT char *msStripPath(char *fn);
-  MS_DLL_EXPORT char *msGetPath(char *fn);
+  MS_DLL_EXPORT char *msGetPath(const char *fn);
   MS_DLL_EXPORT char *msBuildPath(char *pszReturnPath, const char *abs_path, const char *path);
   MS_DLL_EXPORT char *msBuildPath3(char *pszReturnPath, const char *abs_path, const char *path1, const char *path2);
   MS_DLL_EXPORT char *msTryBuildPath(char *szReturnPath, const char *abs_path, const char *path);

mapstring.c

@@ -663,7 +663,7 @@ char *msStripPath(char *fn)
 /*
 ** Returns the *path* portion of the filename fn. Memory is allocated using malloc.
 */
-char *msGetPath(char *fn)
+char *msGetPath(const char *fn)
 {
   char *str;
   int i, length;