first usable version of kernel and commands

After an year of hard work, this is a first "usable" version of Jehanne.

qa/kern/execl.c

@@ -0,0 +1,30 @@
+#include <u.h>
+#include <libc.h>
+
+void
+main(int argc, char *argv[])
+{
+	Waitmsg *w;
+	int i;
+
+	for(i = 0; i < argc; i++){
+		switch(fork()){
+		case -1:
+			fprint(2, "fork fail\n");
+			exits("FAIL");
+		case 0:
+			execl("/cmd/echo", "echo", argv[i], nil);
+			fprint(2, "execl fail: %r\n");
+			exits("FAIL");
+		default:
+			w = wait();
+			if(w->msg[0]){
+				print("FAIL\n");
+				exits("FAIL");
+			}
+			break;
+		}
+	}
+	print("PASS\n");
+	exits("PASS");
+}