Allow color of an HR element to be changed.
Make HR be a block element in quirks mode instead of the hacky inline we were previously using (standards mode already had it as a block).
Patch by Ian Hickson <ian@hixie.ch> with minor modifications by me.
r+sr=bzbarsky@mit.edu
git-svn-id: svn://10.0.0.236/trunk@145375 18797224-902f-48f8-a5cc-f745e15eee43
c8612ff038
