New option to gitmail: summarize commits at the top
New option to gitmail: summarize commits at the top

When the new 'summarythreshold' config option is set, gitmail will
produce a summary at the top of the mail. This consists of the
abbreviated commit hash and first line of the log message (truncated
to 72 characters to look nice in mail)

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome