We're never going to implement the undocumented ones and we're moving 
more and more towards the architecture of the more recent versions of 
native rpcrt4.

Spotted by Ken Thomases.

Convert ex->cb into a character count before assigning it to nCount.

Remove some dubious minus ones that would result in different character 
counts for the Unicode and ANSI paths.

riched20: The wParam parameter to WM_GETTEXT contains the number of characters, not the number of bytes.

Fix up some places in the WM_GETTEXT handler where it was assumed that 
it was a byte count.

Based on a patch by Kris Moore.

Spotted by Christoph von Wittich <Christoph@ApiViewer.de>.