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 signal.c to ignore SIGPIPE signals.  On a network disconnect, a SIGPIPE signal occurs in the write system call when SSL_shutdown attempts to send a "close notify" alert to the peer while the socket is in a disconnected state.  FreeRDP core treats the SIGPIPE signal as a fatal error and silently exits the process.  The proper way to handle this error condition is to ignore the SIGPIPE signal and allow the write system call to fail gracefully with an errno of EPIPE.

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.