handlers.
+ Disentangle all box tree manipulation from browser window
code and put it where it belongs.
+ Move other content specific and other irrelevant code from
browser window handling to appropriate places.
+ Put mouse state enum in new mouse header, since it's not just
used by browser window code, and it is used by treeview
windows on the treeview branch.
svn path=/trunk/netsurf/; revision=10561
Michael Drake