gitweb: Add title attribute to ref marker with full ref name

gitweb: Add title attribute to ref marker with full ref name

Add title attribute, which will be shown as popup on mouseover in
graphical web browsers, with full name of ref, including part (type)
removed from the name of ref itself. This is useful to see that this
strange ref is StGIT ref, or it is remote branch, or it is lightweigh
tag (with branch-like name).

Signed-off-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>