Explicitly state that used /bin/bash shell in Makefile

Code

    $(shell if [[ `tar --version` =~ "bsdtar" ]]; ...

written using Bash double-bracket conditions syntax.  When (default on
some platforms) /bin/sh interpreter used this code outputs error (but
luckily works as required):

    /bin/sh: 1: [[: not found
Use declaration-time expansion assignment for $(shell ...) variables

Not important in this case actually, but recommended for such cases in
general (so that shell expression evaluated only once).
Use make conditions instead bash conditions

Suggested by @jpommerening.
Add missed spaces around ':='
Merge branch 'fix_docs_makefile' of git://github.com/vrutsky/buildbot
Don't overwrite RETRY status when handling interrupts.
Merge branch 'dont-override-retry' of git://github.com/bhearsum/buildbot
ignore http proxy env variables during http step tests

When running unit tests of buildbot.steps.http, ignore http
proxy environment variables. Otherwise tests will try to make
http requests via proxy if for example 'http_proxy' variable
is set.
Merge branch 'http-step-proxy' of git://github.com/elmirjagudin/buildbot
checkfiles: git hook to run autopep8 + automatic import reordering

usage:

for one file:
echo master/buildbot/process/buildstep.py | common/checkfiles
for all files:
find . -name \*.py | common/checkfiles

as a git hook:
cp common/hooks/post-commit .git/hooks

After you do your commit, the script will run on the modified files
You see the results in the terminal, you can review it, and amend your patch

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
autopep8 on everything

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
fix issues from autopep8

- from __future__ needs to be first import
- dont enforce is None for sqlalchemy code
- support '__contains__' for PropertyMixin on top of 'has_key',
  so that autopep8 change from has_key to 'in' works
- use isinstance instead of type(x) in types.StringTypes
- fix one meaningful trailing space in a multiline string
- fix unused import types errors

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
REVERTME: revert autopep8 stuff that breaks on 2.5

use except E,e: syntax
dont import functools reduce
fix python2.5 lack of 3.0 octal syntax

revert when we drop support for 2.5

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>