Fixed SYSENTER, SYSEXIT, SYSCALL, and SYSRET;

SYSCALL and SYSRET are now perfectly in line with AMD's specification;
Improvements to the API call to gracefully stop the emulator.

src/pc.c

@@ -835,6 +835,8 @@ pc_reset_hard_init(void)
 
     atfullspeed = 0;
     pc_full_speed();
+
+    cycles = cycles_main = 0;
 }