{ood,sources,targets}: fix relative paths; turn missing targets into sources.

When we check dependencies and a previously-is_generated dependency
existed before, but no longer does, forget that it was is_generated.
This slightly improves the situation where as a project evolves, a file
that used to be a target gets removed, and then later is re-added as a
static source file.  (It doesn't fix the other variant, where a file is
changed from target to source in a single atomic change, and is never
missing.  That one will be trickier to handle.)

While adding a test for this behaviour, I discovered that redo-sources,
redo-targets, and redo-ood were reporting their output relative to
STARTDIR instead of relative to $PWD, so fix that too.

redo-ood.py

@@ -21,9 +21,10 @@ def set_checked(f):
     cache[f.id] = 1
 
 
+cwd = os.getcwd()
 for f in state.files():
     if f.is_generated and f.read_stamp() != state.STAMP_MISSING:
         if deps.isdirty(f, depth='', max_changed=vars.RUNID,
                         already_checked=[],
                         is_checked=is_checked, set_checked=set_checked):
-            print f.nicename()
+            print state.relpath(os.path.join(vars.BASE, f.name), cwd)