added screen affinity to Group

Closes #323
fix some race conditions when maximize/fullscreen and change group

also should fix maximization/fullscreen in windows of not managed groups

Closes #326
added bitcoin ticker widget
added missing import in __init__.py for widget bitcoin ticker
fixing small typo in the documentation of the float_types
fix _dirGroup()
Adding iface automatic detection for NetGraph

Uses /proc, so it's linux only.

Closes #334
Adding HDDBusyGraph to widgets

Closes #333
Preventing NotificationService from registering if unused

Until now, once libqtile.widget was imported, a new NotificationService was
created and registered as a DBus Notification daemon, and thus making
impossible for any other notification daemon to register.

This patch prevents NotificationManager.service (a NotificationService
instance) to be initialized until further call of register() method, which
basically avoid registering as a notification daemon when the configuration
does not uses any notification widget.

Closes #335
Adding keyboard layout widget

Closes #337
PPA includes a Raring (13.04) version.

Closes #339
Version bump for saucy salamander

Also add howto for packaging so I don't forget how next time :-)
Remove TODO from debian docs
Merge branch 'master' into develop
Code formatting

Closes #332
Don't die on all exceptions

This is annoying, since most things are just stuff we haven't anticipated. Yes,
you can probably get into some unrecoverable states, but it's highly likely
you'll be able to save your work and exit gracefully, instead of just having
the WM crash hard.

Also, catch a BadDrawables, since they're products of the same race as
BadAccess and BadWindow.

Closes #340
Fix typo
Fix multiple matching for dynamic groups.

Initial problem:
    Qtile proceeded matching rules until the end.
Example:
    When matching weechat in a first group and xterm in a second one,
    weechat will be setup into the second group.

New behaviour:
    Qtile stops matching after first result.
Example:
    Weechat matchs the first group and the matching process stops.

Closes #342
added DF to widget.__init__
added disk free widget