Include Dev12 support

Added Dev12 support to my 2012 manifest file.  Already supported in the
main tree.  This just allows for easier dogfooding from Visual Studio
Block caret height problem

The block caret height calculation was using the Height property of the
character bounds.  This will actually return the height of the entire
line and not the text.  The height of the line can be substantially
higher than the text if there are margins.  Switching to using
TextHeight instead