added reenter check to lock_dequeue() to avoid unlocking of interrupts

via cause_sig() during an exception.

moved lock check configuration to <minix/sys_config.h> instead of
kernel/config.h, because the 'relocking' field in kinfo depends on it.

other prettification: common locking macro, whether lock timing is on or
not.

include/minix/sys_config.h

@@ -68,4 +68,7 @@ error "In <minix/sys_config.h> please define _MINIX_MACHINE to have a legal valu
 error "_MINIX_MACHINE has incorrect value (0)"
 #endif
 
+/* Kernel debug checks */
+#define DEBUG_LOCK_CHECK 0	/* Interrupt Lock/unlock sanity checking. */
+
 #endif /* _MINIX_SYS_CONFIG_H */

include/minix/type.h

@@ -104,7 +104,9 @@ struct kinfo {
   int nr_tasks;			/* number of kernel tasks */
   char release[6];		/* kernel release number */
   char version[6];		/* kernel version number */
-  int relocking;		/* relocking check (for debugging) */
+#if DEBUG_LOCK_CHECK
+  int relocking;		/* interrupt locking depth (should be 0) */
+#endif
 };
 
 /* Load data accounted every this no. of seconds. */