Improving diffconflicts to handle diff3 conflictstyle

I cleaned up and simplified diifconflicts to handle diff3 conflictstyle.  I also removed all 3-way diffs since vim displays those so poorly.  I replaced the 3-way diff with 2 more tab pages one to display the 2-way diff of LOCAL to BASE and the other to display the 2-way diff of REMOTE to BASE.  The script also now works no matter which conflictstyle is set in git config.