use const for switch_core_permanent_strdup var.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@4220 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/include/switch_core.h

@@ -375,7 +375,7 @@ SWITCH_DECLARE(void *) switch_core_session_alloc(switch_core_session_t *session,
   \param todup the string to duplicate
   \return a pointer to the newly duplicated string
 */
-SWITCH_DECLARE(char *) switch_core_permanent_strdup(char *todup);
+SWITCH_DECLARE(char *) switch_core_permanent_strdup(const char *todup);
 
 /*! 
   \brief Copy a string using memory allocation from a session's pool

src/switch_core.c

@@ -1443,7 +1443,7 @@ SWITCH_DECLARE(void *) switch_core_permanent_alloc(switch_size_t memory)
 	return ptr;
 }
 
-SWITCH_DECLARE(char *) switch_core_permanent_strdup(char *todup)
+SWITCH_DECLARE(char *) switch_core_permanent_strdup(const char *todup)
 {
 	char *duped = NULL;
 	switch_size_t len;