Pick up where i left off in april:

- move log into metadata part of disk, so that marking
that the log's blocks are in use falls out for free
- superblock describes the whole disk (sizes and offets)
- sizes and offsets are computed in one place (mkfs) and
the rest of the code refers to the superblock for these values,
instead of recomputing them.

proc.c

@@ -339,7 +339,8 @@ forkret(void)
     // of a regular process (e.g., they call sleep), and thus cannot 
     // be run from main().
     first = 0;
-    initlog();
+    iinit(ROOTDEV);
+    initlog(ROOTDEV);
   }
   
   // Return to "caller", actually trapret (see allocproc).