TST is supposed to set negative flag as well

[harbaum]

The TST instruction is supposed to set the Zero and the Negative flag. This one here only sets zero which makes the atari st ikbd rom mouse reporting fail as this test:

fb39	96 c9		ldaa c9				;$C9 Mouse mode
...
fb3f	4d		tsta			
fb40	2a 1a		bpl  1a (FB5C)	

always fails and the branch is taken even if the value read from $c9 is negative.

This can be fixed by changing https://github.com/thasega/HD63701/blob/master/HD63701_EXEC.v#L147 to

`mcTST: rC   <= {rC[5:4],CC[3:2],rC[1:0]};

[harbaum]

This has also been fixed in https://github.com/harbaum/ikbd