kernel: some boottime sanitychecks

. Check if we have the right number of boot modules
	. Check if the ELF parsing of VM actually succeeded

Both these are root causes of less-than-obvious other
errors/asserts a little further down the line; uncovered
while experimenting with booting by iPXE, specifically
(a) iPXE having a 8-multiboot-modules limit and
(b) trying to boot a gzipped VM.

kernel/main.c

@@ -143,6 +143,10 @@ void kmain(kinfo_t *local_cbi)
 
    proc_init();
 
+   if(NR_BOOT_MODULES != kinfo.mbi.mods_count)
+   	panic("expecting %d boot processes/modules, found %d",
+		NR_BOOT_MODULES, kinfo.mbi.mods_count);
+
   /* Set up proc table entries for processes in boot image. */
   for (i=0; i < NR_BOOT_PROCS; ++i) {
 	int schedulable_proc;