Insert-Symbol-Enhancement

Hi,
this patch enhance the gtk-insert-symbol-dialog.
Here is the list of the new features:
- shows all characters of a font (scrollbar)
- resize correct
- don't crash if you try to insert a non existing character.

I need such a version of insert-symbol (not the gucharmap) because some
dingsbats-fonts are not usable with gucharmap. Gucharmap had other
issues, that if you select a character not in the chosen font you get
wired things.

This patch may break some non unix-builds, but I have not tested that.

Michael

PS: this version take so long, because I made holidays... (without computer)