very long data urls break inline history, currently in two ways.
first, the split url isn't joined when displayed, resulting in multiple inline history lines.
second, very long urls are displayed in full, resulting in ugliness.
see bug 804961 for an example.
oops, bug 804946
the first half will be fixed by bug 772359
Should we also block URLs over some length, like 2048 characters?
Committing to: bzr+ssh://email@example.com/bmo/4.2/
Committed revision 9020.