Create new postCallback() helper method

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

libsuperuser is currently able to handle failures in several different
stages:

1) If the shell cannot be started at all (e.g. missing "su" binary),
Runtime.exec() should throw an exception, causing our open() method to
return failure.

2) 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.

3) If the device operator denies a Superuser request, this typically
falls under case #2 as the "su" executable will stay alive for a couple
of seconds until the operator clicks "deny."

But if the shell dies when there is no active command, any 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
operator kills it, resulting in a subpar user experience.

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 instantly denies root access to all
apps).  It will hang at "Requesting root privilege" forever.

So, we'll add an extra loop to send the bad news to the calling app if
libsuperuser isn't able to execute the requested commands.
Run dos2unix on *.java

Currently these source files have a mix of CRLF and LF (even inside the
same file), which causes problems with patching/merging.  Pick one format
for consistency's sake.
Merge pull request #8 from cernekee/missing-callbacks-v1

Looks good to me