Remove ISDN hold restriction for non-bridged calls.

The check if an ISDN call is bridged before it could be placed on hold is
not necessary and is overly restrictive.  The check was originally done to
prevent problems with call transfers in case a user tried to transfer a
call connected to an application to another call connected to an
application.  The ISDN transfer code has not required this restriction for
quite some time because ECT could transfer any two active calls to each
other.

* Remove ISDN hold restriction for calls connected to applications.

* Made ast_waitfordigit_full() ignore AST_CONTROL_HOLD and
AST_CONTROL_UNHOLD instead of generating a warning message.

(closes issue ASTERISK-19388)
Reported by: Birger Harzenetter
Tested by: rmudgett
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Merged revisions 357894 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 357895 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@357896 65c4cc65-6c06-0410-ace0-fbb531ad65f3