If a user manually changes a generated file, don't ever overwrite it.

That way the user can modify an auto-generated 'compile' script, for
example, and it'll stay modified.

If they delete the file, we can then generate it for them again.

Also, we have to warn whenever we're doing this, or people might think it's
a bug.

builder.py

@@ -42,6 +42,10 @@ def _try_stat(filename):
             raise
 
 
+def warn_override(name):
+    warn('%s - you modified it; skipping\n' % name)
+
+
 class ImmediateReturn(Exception):
     def __init__(self, rv):
         Exception.__init__(self, "immediate return with exit code %d" % rv)
@@ -69,6 +73,16 @@ class BuildJob:
                 return self._after2(0)
         except ImmediateReturn, e:
             return self._after2(e.rv)
+        newstamp = sf.read_stamp()
+        if (sf.is_generated and
+            not sf.failed_runid and
+            newstamp != state.STAMP_MISSING and 
+            (sf.stamp != newstamp or sf.is_override)):
+                warn_override(_nice(t))
+                sf.set_override()
+                sf.set_checked()
+                sf.save()
+                return self._after2(0)
         if (os.path.exists(t) and not os.path.exists(t + '/.')
              and not sf.is_generated):
             # an existing source file that was not generated by us.
@@ -87,7 +101,6 @@ class BuildJob:
         (dofile, basename, ext) = _find_do_file(sf)
         if not dofile:
             if os.path.exists(t):
-                sf.is_generated = False
                 sf.set_static()
                 sf.save()
                 return self._after2(0)
@@ -176,7 +189,7 @@ class BuildJob:
             else:
                 unlink(tmpname)
             sf = self.sf
-            sf.is_generated=True
+            sf.is_generated = True
             sf.update_stamp()
             sf.set_changed()
             sf.save()