add switch_stristr and use it in dptools

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@5887 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/include/switch_utils.h

@@ -298,6 +298,8 @@ if (vname) {free(vname); vname = NULL;}vname = strdup(string);}
 */
 SWITCH_DECLARE(unsigned int) switch_separate_string(char *buf, char delim, char **array, int arraylen);
 
+SWITCH_DECLARE(const char *) switch_stristr(const char *str, const char *instr);
+
 /*!
   \brief Escape a string by prefixing a list of characters with an escape character
   \param pool a memory pool to use