Addition of auto reconnect to FreeRDP core and X11 client

Added auto reconnect capability to FreeRDP core and X11 client.  Changes included the following:
1.  Added public freerdp_reconnect function to FreeRDP core along with corresponding lower level logic.
2.  Modified tcp.c to implement earlier network break detection via additional keep alive options.
3.  Updated the X11 client to implement auto reconnect.
4.  Modified tls.c to prevent a crash in SSL_shutdown after a network disconnect.

Note that without additional keep alive options, Ubuntu 12.04 would take anywhere from 10 to 15 minutes to detect a network break with the current source in FreeRDP master.  With the added keep alive options, the network break detection is now roughly 15 seconds.