state.stamp() can't imply state.built().

...because we deliberately stamp non-generated files as well, and that
doesn't need to imply that we rebuilt them just now.  In fact, we know for a
fact that we *didn't* rebuild them just now, but we still need to record the
timestamp for later.

builder.py

@@ -139,6 +139,7 @@ class BuildJob:
                 os.rename(tmpname, t)
             else:
                 unlink(tmpname)
+            state.built(t)
             state.stamp(t)
         else:
             unlink(tmpname)

state.py

@@ -71,7 +71,6 @@ def _stampname(t):
     
 
 def stamp(t):
-    built(t)
     mark(t)
     stampfile = _stampname(t)
     newstampfile = _sname('stamp' + str(os.getpid()), t)