Fixed page up/page down in text editor: confusion between character and pixel coordinates caused caret to move to the wrong column.
Fixed crash when StartProgram or WorkingDirectory were invalid paths.
git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@2990 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61