New features for debcheckout, ... now with TopGit support!

Today I've spent some time hacking on debcheckout, which for weird reasons happens to be at the bottom of a stack of chained things that I need to do in the forthcoming days. Also, I had neglected debcheckout for a while, and the other devscripts folks where ready to shout at me because of that :-) .

Well, it has been fun, and beside having fixed all the outstanding bugs, debcheckout has grown some cute new features:

the ability to query a VCS repository (using -d/--details) for details, at the very minimum it will parse for you the Vcs-* fields, but it is expected that in the future will be able to be more telling, and it is already so for TopGit ...
... and speaking about that, debcheckout now has support for TopGit. In two ways: the first one is using -d, which will tell you whether a GIT repo is TopGit-enabled or not and, if it is so, also the list of available top-bases. For instance:
```
  zack@usha:~$ debcheckout -d topgit
  type    git
  url     git://git.debian.org/git/collab-maint/topgit.git
  top-bases       debian/locations
  topgit  yes
```
or even more brutally
```
   zack@usha:~$ debcheckout -d git://git.debian.org/git/pkg-ocaml-maint/packages/ocaml-batteries.git
   type    git
   url     git://git.debian.org/git/pkg-ocaml-maint/packages/ocaml-batteries.git
   top-bases       features/flexi-build
   topgit  yes
```
The other way in which TopGit is supported, is that when checking out a GIT repo which is detected to be TopGit's as well, population of top-bases (i.e., TopGit local initialization) is automatically performed.

... yes, a while ago I've fallen in love with TopGit, is it that evident?
it is now possible to specify custom rules for authenticated mode, this way you can use -a also on packages not hosted on well known Debian/Ubuntu VCS servers
finally, you can now ask debcheckout to automatically enable remote tracking of remote GIT branches, which is usually what a maintainer wants to do when doing a fresh checkout

Enjoy!

(ah, of course all this is not uploaded yet, but you can grab a preview from devscripts' VCS or, better, doing debcheckout devscripts which is soooo bootstrapy. SCNR.)