Escaping in (#51382)

[Owen Taylor <otaylor redhat com>]

Bug 51382 points out that there is no way to indicate
literal '/' characters in a GtkItemFactoryEntry.

(On a related topic, there is also a bug so that when 
turning item factory strings entries into paths, 
"/File/Add __" gets turned to "/File Add " not
"/File Add _"

And a bug where gtk_item_factory_print_func doesn't
handle an itemfactory entry containing literal \n.)

We don't really have an escaping standard in GTK+:

 * GScanner and hence RC files support C-string like
   escaping with \n \r \t \b \f and octal escapes.

   This would imply:

   "/_File/\\/var\\/log\\/messages"

 * GMarkup, and hence markup-labels, uses, XML/SGML
   entities, so:

   "/_File/&#2f;var&#2f;log&#2f;messages"

I think the first one is probably a bit more expected
and less unreadable so I'll suggest that we should do 
that.

Regards,
                                        Owen