About refs refs/heads/+...

I accidentally created a branch whose name starts with "+". Everything went ok until I pushed it because "+" is interpreted as forced refspec (e.g. "git push somewhere +wip"). Using full ref names would avoid ambiguity. The corner case of this is where the branch name is simply "+". Then refspec "+:" will be interpreted completely different from what the user wants. I wonder if we could do something better:

 - forbid "/+" in ref names (too strong?)
 - some heuristics to detect "+:" and refuse it if ref "+" exists.
heuristics to hint the user about full ref name after we fail to match
refspec because we misinterpret "+"
 - improve refspec matching code to detect ambiguation and force using
full ref name.