rdesktop 1.7.1

Current rdesktop 1.8 does not work properly on OSX, in particular
keyboard and mouse events are not beint sent. See official issue:
http://sourceforge.net/p/rdesktop/bugs/376/

This commit reverts to 1.7.1 and fixes an issue with missing
symbols.

Closes #28260.
Closes #27947.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>