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).

qa/lib/c/lockt.c

@@ -16,7 +16,7 @@
  * along with Jehanne.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include <u.h>
-#include <libc.h>
+#include <lib9.h>
 
 QLock rl;
 Rendez rStart;
@@ -85,7 +85,7 @@ main(void)
 	resInWaiter = 0xff;
 
 	spawnWaiter(&l);
-	lock(&l);
+	jehanne_lock(&l);
 
 	alarm(20000);	/* global timeout, FAIL if reached */
 	if (!atnotify(failOnTimeout, 1)){
@@ -112,7 +112,7 @@ main(void)
 	rwakeupall(&rStart);
 	qunlock(&rl);
 	sleep(1200);
-	unlock(&l);
+	jehanne_unlock(&l);
 
 	qlock(&rl);
 	while(elapsedInWaiter == 0)