* pango/Makefile.am: add Matrix.custom
* pango/Matrix.custom: add Pango.Matrix.Identity field
which is the equivalent of PANGO_MATRIX_INIT
* sample/GtkDemo/DemoRotatedText.cs: use Pango.Matrix.Identity
* doc/en/Pango/Matrix.xml: add docs for Pango.Matrix.Identity
svn path=/trunk/gtk-sharp/; revision=44181