Update sysutils/fabric to 1.4.2

Upstream changes:
-----------------

:release:`1.4.2 <2012-05-07>`
:release:`1.3.7 <2012-05-07>`
:bug:`562` Agent forwarding would error out or freeze when multiple uses of the
forwarded agent were used per remote invocation (e.g. a single
~fabric.operations.run command resulting in multiple Git or SVN checkouts.)
This has been fixed thanks to Steven McDonald and GitHub user @lynxis.

:support:`626` Clarity updates to the tutorial. Thanks to GitHub user m4z for
the patches.

:bug:`625` ~fabric.context_managers.hide/~fabric.context_managers.show did not
correctly restore prior display settings if an exception was raised inside the
block. This has been fixed.

:bug:`624` Login password prompts did not always display the username being
authenticated for. This has been fixed. Thanks to Nick Zalutskiy for catch &
patch.

:bug:`617` Fix the clean_revert behavior of ~fabric.context_managers.settings
so it doesn't KeyError for newly created settings keys. Thanks to Chris
Streeter for the catch.

:feature:`615` Updated ~fabric.operations.sudo to honor the new setting
:ref:`env.sudo_user <sudo_user>` as a default for its user kwarg.

:bug:`616` Add port number to the error message displayed upon connection
failures.

:bug:`609` (and :issue:`564`) Document and clean up :ref:`env.sudo_prefix
<sudo_prefix>` so it can be more easily modified by users facing uncommon use
cases. Thanks to GitHub users 3point2 for the cleanup and SirScott for the
documentation catch.

:bug:`610` Change detection of env.key_filename's type (added as part of SSH
config support in 1.4) so it supports arbitrary iterables. Thanks to Brandon
Rhodes for the catch.


(gls)