Drop time-stamp comparison, remove variable comments from generated files.

See discussion at http://tickets.musicbrainz.org/browse/PICARD-566

setup.py

@@ -311,8 +311,13 @@ class picard_build_ui(Command):
             tmp = StringIO()
             uic.compileUi(uifile, tmp)
             source = tmp.getvalue()
+            rc = re.compile(r'\n\n#.*?(?=\n\n)', re.MULTILINE|re.DOTALL)
+            comment = (u"\n\n# Automatically generated - don't edit.\n"
+                       u"# Use `python setup.py %s` to update it."
+                       % _get_option_name(self))
             for r in list(_translate_re):
                 source = r.sub(r'_(\1)', source)
+                source = rc.sub(comment, source)
             f = open(pyfile, "w")
             f.write(source)
             f.close()
@@ -322,7 +327,6 @@ class picard_build_ui(Command):
                 compile_ui(uifile, pyfile)
         else:
             for uifile, pyfile in ui_files():
-                if newer(uifile, pyfile):
                compile_ui(uifile, pyfile)
 
         from resources import compile, makeqrc