Fixed typo srting -> string.

Added support for passing in a file or StringIO handle.

E.g.:
from cStringIO import StringIO
from sshpt import sshpt

out=StringIO()
output_queue = sshpt( ...params, outputhandle=out)
output_queue.join()
print "[%s]" % out.getvalue()
Combine stderr into stdout via pty.
Added a exec_command_combine_stderr for testing.
This doesn't preserver order like via pty.
Normal commands run via pty.
Commands via sudo run without pty but append stderr to stdout output (i.e. order isn't preserved).
Remove -k from sudo. Not supported everywhere :(
Don't use via_pty for how. Pty seems to add newlines when I don't want it to.
Merge pull request #1 from ruivapps/outputhandle

outputhandle branch