[Pidgin] #3467: Fix IRC handling of mIRC formatting

[Pidgin]

#3467: Fix IRC handling of mIRC formatting
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 Reporter:  rekkanoryo  |       Owner:  elb  
     Type:  patch       |      Status:  new  
 Priority:  minor       |   Milestone:  2.2.2
Component:  IRC         |     Version:  2.2.1
 Keywords:              |     Pending:  0    
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 This patch effectively copies an older version of glib's
 `g_markup_escape_text()` and its private helper function
 `append_escaped_text()` that ignores the control characters mIRC uses.
 Recent versions of glib (anything released on or after 2007-08-09) have
 different behavior that causes these characters to be converted to XML
 entities (see GNOME bug [GnomeBug:464145 464145] and glib's SVN
 [http://svn.gnome.org/viewcvs/glib/trunk/glib/gmarkup.c?r1=5604&r2=5684
 revision 5684] for details on the change).

 I'm not convinced this is the correct fix, but it works, and we were
 technically relying on the bug in the older version of
 `append_escaped_text()`.

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Ticket URL: <http://developer.pidgin.im/ticket/3467>
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