Document BLINDTRANSFER behavior change.

(issue ASTERISK-19322)

(closes issue ASTERISK-19875)
Reported by: call
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Merged revisions 368469 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 368470 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@368472 65c4cc65-6c06-0410-ace0-fbb531ad65f3

UPGRADE.txt

@@ -25,6 +25,11 @@ From 10 to 11:
 Parking:
  - The comebacktoorigin setting must now be set per parking lot. The setting in
    the general section will not be applied automatically to each parking lot.
+ - The BLINDTRANSFER channel variable is deleted from a channel when it is
+   bridged to prevent subtle bugs in the parking feature.  The channel
+   variable is used by Asterisk internally for the Park application to work
+   properly.  If you were using it for your own purposes, copy it to your
+   own channel variable before the channel is bridged.
 
 res_ais:
  - Users of res_ais in versions of Asterisk prior to Asterisk 11 must change