- panic if there's no runnable process

- more basic sanity check before recursive enter check (data segment)
 - try to jump to boot monitor instantly on recursive panic

kernel/glo.h

@@ -58,6 +58,8 @@ EXTERN time_t boottime;
 EXTERN char params_buffer[512];		/* boot monitor parameters */
 EXTERN int minix_panicing;
 EXTERN int locklevel;
+#define MAGICTEST 0xC0FFEE23
+EXTERN u32_t magictest;			/* global magic number */
 
 #if DEBUG_TRACE
 EXTERN int verboseflags;