cmds: check for errors when visualizing history

Catch exceptions when launching a history browser so that the user can
know when a browser has not been configured.

Closes #226

Reported-by: Benoît Nouyrigat @bnouyrigat via github.com
Signed-off-by: David Aguilar <davvid@gmail.com>
app: replace core.setenv with compat.setenv
compat: replace os.environment with os.environ
core: replace cmd with argv
interaction: add missing argument in confirm_config_action()
models.browse: replace NotImplemented with NotImplementedError
widgets.spellcheck: fix context_menu() call in contextMenuEvent()
widgets.archive: fix name conflict in GitArchiveDialog

Rename GitArchiveDialog.save() to GitArchiveDialog.save_hashed_objects().
widgets.main: replace editremotes.edit() with editremotes.remote_editor()
widgets.standard: refactor widgets generated with bind_mixin() for pylint
cmds: fix bug in OpenParentDir()

When OpenParentDir() runs, it will try to concatenate a set with a list
and subsequently fail with a dialog box.
doc: add Alex to the credits

Signed-off-by: David Aguilar <davvid@gmail.com>
Merge branch 'pylint'

Lots of pylint fixes courtesy of Alex Chernetz.

* pylint:
  doc: add Alex to the credits
  cmds: fix bug in OpenParentDir()
  widgets.standard: refactor widgets generated with bind_mixin() for pylint
  widgets.main: replace editremotes.edit() with editremotes.remote_editor()
  widgets.archive: fix name conflict in GitArchiveDialog
  widgets.spellcheck: fix context_menu() call in contextMenuEvent()
  models.browse: replace NotImplemented with NotImplementedError
  interaction: add missing argument in confirm_config_action()
  core: replace cmd with argv
  compat: replace os.environment with os.environ
  app: replace core.setenv with compat.setenv

Closes #227

Signed-off-by: David Aguilar <davvid@gmail.com>
README.md: title-case Git
doc: update v1.9.4 release notes
dag: remove references to self.Mixin

The old bind_mixin() setup in cola.widgets.standard provided self.Mixin
as a way to refer to the widget-specific mixin class.

This is no longer needed since we can simply refer to the base
class instead.  In hindsight, we probably could have done without
this all along, but it was written the long-hand way before to avoid
any confusion about which method is being called.

Signed-off-by: David Aguilar <davvid@gmail.com>
doc: add missing sub-commands to the man page

Signed-off-by: David Aguilar <davvid@gmail.com>
doc: use https:// URLs in the introduction

Signed-off-by: David Aguilar <davvid@gmail.com>
qtutils: refactor widget save/restore methods into the base classes

Move all of the qtutils functions related to saving and restoring widget
state into the widgets.standard base classes.  This means that
widgets.standard no longer depends on qtutils, and qtutils no longer
depends on settings.

Signed-off-by: David Aguilar <davvid@gmail.com>
merge: use the mac metal style on OS X

Signed-off-by: David Aguilar <davvid@gmail.com>