Be consistent, send From: "Anonymous" <sip:anonymous@anonymous.invalid>

When setting CALLERID(pres)=unavailable in the dialplan, the From header
in the SIP message contains "Anonymous" <sip:Anonymous@anonymous.invalid>.
For consistency, Asterisk should use a lowercase a in the userpart of the
URI.

* Make the From header use a lowercase A in the userpart of the anonymous
URI.

(closes issue ASTERISK-19838)
Reported by: Antti Yrjola
Patches:
      chan_sip_patch_ASTERISK-19838.patch (license #6383) patch uploaded by Antti Yrjola
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Merged revisions 373500 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 373501 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 373502 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@373503 65c4cc65-6c06-0410-ace0-fbb531ad65f3