[Fixes#70187]. Kill two varargs warnings.
* gtk/TextBuffer.custom: Update for that, and also implement
InsertWithTagsByName
* sample/GtkDemo/DemoHyperText.cs:
* sample/GtkDemo/DemoTextView.cs: Remove kludges for broken
TextIter handling. Also fix the i18n demo bits by translating the
octal-encoded UTF-8 to hex-encoded UTF-16.
svn path=/trunk/gtk-sharp/; revision=37039