Various build fixes for Qt5 support
Force the case of dictionary words, to avoid weird sorting issues
Improve error an message
When reporting the column number, start counting at 1 instead of 0.

This is more user-friendly.
Add a PNG icon, used instead of the XPM one on Debian systems.

This fixes a strange stretching of the icon in the Gnome 2 quickstart bar.
Fix conditional build of the Qt interface