Update documentation for MessageSend application/command's From field for XMPP

When using the channel technology agnostic application/AMI command MessageSend,
the "From" field is technically optional for the SIP channel driver.  However,
if being sent by the XMPP resource module (either res_xmpp or res_jabber), the
"From" field is necessary, and must correspond to a defined account.  This
patch updates the documentation for this application/AMI command to reflect
this.

(closes issue ASTERISK-20405)
Reported by: Leif Madsen
........

Merged revisions 374611 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@374612 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/message.c

@@ -129,6 +129,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 				<para>A From URI for the message if needed for the
 				message technology being used to send this message.</para>
 				<xi:include xpointer="xpointer(/docs/info[@name='SIPMessageFromInfo'])" />
+				<xi:include xpointer="xpointer(/docs/info[@name='XMPPMessageFromInfo'])" />
 			</parameter>
 		</syntax>
 		<description>
@@ -171,6 +172,7 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 				<para>A From URI for the message if needed for the
 				message technology being used to send this message.</para>
 				<xi:include xpointer="xpointer(/docs/info[@name='SIPMessageFromInfo'])" />
+				<xi:include xpointer="xpointer(/docs/info[@name='XMPPMessageFromInfo'])" />
 			</parameter>
 			<parameter name="Body">
 				<para>The message body text.  This must not contain any newlines as that

res/res_xmpp.c

@@ -284,6 +284,11 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 		<para>Specifying a prefix of <literal>xmpp:</literal> will send the
 		message as an XMPP chat message.</para>
 	</info>
+	<info name="XMPPMessageFromInfo" language="en_US" tech="XMPP">
+		<para>Specifying a prefix of <literal>xmpp:</literal> will specify the
+		account defined in <literal>xmpp.conf</literal> to send the message from.
+		Note that this field is required for XMPP messages.</para>
+	</info>
 ***/
 
 /*! \brief Supported general configuration flags */