increasing the python requirement

[Anteru]

> By reducing to 2.6/2.7 we also narrow the gap with python-3.x which
> should make the transition easier.

As an occasional bug fixer and bzr user; I'd be more than happy to see
Bzr to move to Python 2.6 or even 3. The reason is that I typically run
a (more or less recent) 2.x installation for mucking around with various
libraries (2.6 on all Linux installations I use, and 2.7 on Windows) and
the latest stable 3.x for new development.

I haven't run into an issue where something I wanted to contribute to
Bzr got refused because it doesn't work with Python 2.3 or so, but for
me at least it would be much easier if I wouldn't have to worry about
those versions. Sure, I know there are people running RHEL 4 still and
are stuck with ancient Python installations by default -- but how
complicated is it to get a newer Python running side-by-side with the
old one? At least on Windows and Ubuntu, it's pretty easy to have Python
2.x and 3.x installed (on Windows, the Python version shouldn't matter
anyway as it's bundled with the Bzr installer.)

There's definitely nice stuff in 2.6 and 3.x in particular; and in the
future, the LLVM backend for 3.x might allow Bzr to gain quite a bit of
speed with no additional development effort.

Just my two cents,
  Cheers,

  Anteru