TS Gateway Fix, Valgrind Cleanup, Asynchronous Mode (Experimental)

TS Gateway:
base64 encoding was broken, breaking authentication for NTLM messages of a size matching size(msg) = 2 + 4*n. This means all the previous NTLM "fixes" weren't fixing anything, they were just changing the length of the message until some configuration gave a length that was properly encoded.

Valgrind:
Spent some time cleaning up various valgrind complaints

Asynchronous mode:
Use +async-update and +async-input with xfreerdp to experiment with this mode. Updates are queued and dequeued asynchronously with a performance gain. However, there are still race conditions to be fixed, so it is not yet enabled by default.