Documentation reads as:

[...]
  Trac can visualize contents of many Version Control Systems (vcs)
repositories. By default it supports Subversion or Git. Plugins can be
added to support bzr (trac-bzr) or Mercurial (trac-mercurial).
[...]

It is not clear to me if I should install `trac-git` then to get git
support ? Should instead trac-git removed from debian ?

Thanks for clarification.

Some more details:

        trac-admin /path/to/env deploy /path/to/www/trac

should really be read (within the context) as:

        trac-admin /path/to/projectenv deploy /path/to/www/trac

And later on:

#Trac as FastCGI on Apache
#extra info in https://coderanger.net/~coderanger/tracdoc/install/fastcgi.html
ScriptAlias /trac /path/to/www/trac/cgi-bin/trac.fcgi/

should read as:

#Trac as FastCGI on Apache
#extra info in https://coderanger.net/~coderanger/tracdoc/install/fastcgi.html
ScriptAlias /trac /path/to/www/trac/cgi-bin/trac.fcgi/
$ chmod +x /path/to/www/trac/cgi-bin/trac.fcgi

trac-git has finally been removed from jessie.

Dear submitter,

as the package trac has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/948052

The version of this package that was in Debian prior to this removal
can still be found using http://snapshot.debian.org/.

Please note that the changes have been done on the master archive and
will not propagate to any mirrors until the next dinstall run at the
earliest.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmaster@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Scott Kitterman (the ftpmaster behind the curtain)