Switch state.py to use sqlite3 instead of filesystem-based stamps.

It passes all tests when run serialized, but still gives weird errors
(OperationalError: database is locked) when run with -j5.  sqlite3 shouldn't
be barfing just because the database is locked, since the default timeout is
5 seconds, and it's dying *way* faster than that.

redo-ifcreate.py

@@ -5,11 +5,12 @@ from helpers import err, mkdirp
 
 
 try:
+    me = state.File(name=vars.TARGET)
     for t in sys.argv[1:]:
         if os.path.exists(t):
             err('redo-ifcreate: error: %r already exists\n' % t)
             sys.exit(1)
         else:
-            state.add_dep(vars.TARGET, 'c', t)
+            me.add_dep('c', t)
 except KeyboardInterrupt:
     sys.exit(200)