libc: introduce "jehanne_" namespace

With this commit all functions declared in libc.h have been renamed
with the "jehanne_" prefix. This is done for several reason:

- it removes conflicts during symbol resolution when linking
  standard C libraries like newlib or musl
- it allows programs depending on a standard C library to directly
  link to a library depending on our non standard libc (eg libsec).

To ease transiction two files are provided:

- sys/include/lib9.h that can be included instead of <libc.h> to use
  the old names (via a simple set of macros)
- sys/src/lib/c/lib9.c that can be compiled with a program where the
  macro provided by lib9.h are too dumb (see for example rc or grep).

In the kernel port/lib.h has been modified accordingly and some of
the functions it directly provides has been renamed too (eg malloc
in qmalloc.c and print in devcons.c).

sys/src/lib/thread/example.c

@@ -35,12 +35,12 @@ mouseproc(void *arg)
 
 	mc = arg;
 	if((mfd = open("/dev/mouse", OREAD)) < 0)
-		sysfatal("open /dev/mouse: %r");
+		jehanne_sysfatal("open /dev/mouse: %r");
 	for(;;){
 		if(read(mfd, m, sizeof m) != sizeof m)
-			sysfatal("eof");
-		if(atoi(m+1+2*12)&4)
-			sysfatal("button 3");
+			jehanne_sysfatal("eof");
+		if(jehanne_atoi(m+1+2*12)&4)
+			jehanne_sysfatal("button 3");
 		send(mc, m);
 	}
 }
@@ -53,7 +53,7 @@ clockproc(void *arg)
 
 	c = arg;
 	for(t=0;; t++){
-		sleep(1000);
+		jehanne_sleep(1000);
 		sendul(c, t);
 	}
 }
@@ -82,13 +82,13 @@ threadmain(int argc, char *argv[])
 	for(;;){
 		switch(alt(a)){
 		case 0:	/*mouse event */
-			fprint(2, "click ");
+			jehanne_fprint(2, "click ");
 			break;
 		case 1:	/* clock event */
-			fprint(2, "tic ");
+			jehanne_fprint(2, "tic ");
 			break;
 		default:
-			sysfatal("can't happen");
+			jehanne_sysfatal("can't happen");
 		}
 	}
 }