py3: silence warning about deprecation of imp module

Well, we could fix that, but we aren't yet to reach the state caring about
deprecation on the Python 3 line. So let's silence it for now to fix tons
of "minor" Py2/3 incompatibilities by relying on our test suite.

mercurial/util.py

@@ -194,6 +194,9 b' if _dowarn and pycompat.ispy3:'
                             r'mercurial')
     warnings.filterwarnings(r'ignore', r'invalid escape sequence',
                             DeprecationWarning, r'mercurial')
+    # TODO: reinvent imp.is_frozen()
+    warnings.filterwarnings(r'ignore', r'the imp module is deprecated',
+                            DeprecationWarning, r'mercurial')
 
 def nouideprecwarn(msg, version, stacklevel=1):
     """Issue an python native deprecation warning