libsuperuser: Update to upstream rev b1d6c2407a
Fix build failures seen with latest libsuperuser
RootShell: Update to use new libsuperuser logging API
libsuperuser: Create new postCallback() helper method

This just eliminates some repetition.  No change to functionality.
libsuperuser: Missing callbacks if shell dies in Interactive mode

If the shell dies while a command is executing, and the watchdog timer
is enabled, the onCommandResult() callback will get invoked so that the
caller can handle the error.  But if the shell dies between commands,
the queued commands will get stuck in limbo and the caller will never
receive a status indication.  This will probably cause the app to freeze
until the user kills it.

The easiest way to reproduce the problem is to try running
libsuperuser_example in interactive mode on the SDK emulator (which has
a trivial "su" implementation that denies root access to all apps).  It
will hang at "Requesting root privilege" forever.
Bump target API to 19 so we can use KitKat constants
Api: Fix VPN filtering on KitKat

Due to firewall rule changes in KitKat's netd, the outbound interface for
VPN-bound packets shows up as e.g. wlan0 or rmnet0, NOT as tun0.  Add a
new rule to make sure they get handled properly.

See also:
http://forum.xda-developers.com/showthread.php?p=48703545
Merge pull request #242 from cernekee/kitkat-vpn-v1

Fix KitKat VPN; update libsuperuser