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/kern/port/tod.c

@@ -198,7 +198,7 @@ todfix(void)
 
 		/* convert to epoch */
 		mul64fract(&x, diff, tod.multiplier);
-if(x > 30000000000ULL) print("todfix %llud\n", x);
+if(x > 30000000000ULL) jehanne_print("todfix %llud\n", x);
 		x += tod.off;
 
 		/* protect against overflows */