gather 2833 into RTP core and a few tweaks

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@1351 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/include/switch_utils.h

@@ -85,6 +85,13 @@ SWITCH_DECLARE(char) switch_rfc2833_to_char(int event);
 */
 SWITCH_DECLARE(unsigned char) switch_char_to_rfc2833(char key);
 
+/*!
+  \brief determine if a character is a valid DTMF key
+  \param key the key to test
+  \return TRUE or FALSE
+ */
+#define is_dtmf(key)  ((key > 47 && key < 58) || (key > 64 && key < 69) || (key > 96 && key < 101) || key == 35 || key == 42)
+
 /*!
   \brief Duplicate a string 
 */