Fix prototype of sleep() and move it to unistd.h

src/core/misc.c

 /**************************************************************************
 SLEEP
 **************************************************************************/
-void sleep(int secs)
+unsigned int sleep(unsigned int secs)
 {
 	unsigned long tmo;
 
 	for (tmo = currticks()+secs*TICKS_PER_SEC; currticks() < tmo; ) {
 	}
+	return 0;
 }
 
 /**************************************************************************
 void interruptible_sleep(int secs)
 {
 	printf("<sleep>\n");
-	return sleep(secs);
+	sleep(secs);
 }
 
 /**************************************************************************

src/include/etherboot.h

 #include "compiler.h"
 #include "stddef.h"
 #include "stdint.h"
+#include <unistd.h>
 
 
 /*
 
 /* misc.c */
 extern void twiddle P((void));
-extern void sleep P((int secs));
 extern void interruptible_sleep P((int secs));
 extern int strcasecmp P((const char *a, const char *b));
 extern char *substr P((const char *a, const char *b));

src/include/unistd.h

 #include <stddef.h>
 #include <stdarg.h>
 
+extern unsigned int sleep ( unsigned int seconds );
 extern int execv ( const char *command, char * const argv[] );
 
 /**