Scrolling is broken for plain QTextEdit.

This should simplify the merging of the improved lookup context.

Introduced pp-scanner.cpp, renamed `pp' to `Preprocessor' and removed useless #includes.

Removed declaration of slot shadowBuildButtonClicked().

Most desktops allow popups to overlap the taskbar. We should allow this
additional space to be used by the completion popup.

You couldn't disable the 'always adjust column widths to contents' logic
cause of an uninitialized boolean that refused to toggle to false.