[MERGE] Add a way to specify a template commit message

[Alexander Belchenko]

Alexander Belchenko has voted +1 (conditional).
Status is now: Semi-approved
Comment:
For me using variable 'havefile' is slightly spurious. You probably can 
simply join start_message and other subsequent lines together and them 
write them at once to file.
But if other people will satisfied with your patch -- I'm give up.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070204220119.GG3684%40jameswestby.net%3E