importer: reorder/tweak find_module() tests to cope with six.moves

The old hack on the master side we had is broken for some reason on 3.x.
Instead tweak the client to be more selective: if a request is for a
module within a package, the package must be loaded (in sys.modules),
and its __loader__ must be us. Previously if the module didn't exist in
sys.modules, we'd still try to fetch from the master, which doesn't
appear to ever make sense.

mitogen/core.py

@@ -682,27 +682,25 @@ class Importer(object):
 
         _tls.running = True
         try:
-            pkgname, dot, _ = fullname.rpartition('.')
-            _vv and IOLOG.debug('%r.find_module(%r)', self, fullname)
-            suffix = fullname[len(pkgname+dot):]
-            if suffix not in self._present.get(pkgname, (suffix,)):
-                _v and LOG.debug('%r: master doesn\'t know %r', self, fullname)
-                return None
-
-            pkg = sys.modules.get(pkgname)
-            if pkg and getattr(pkg, '__loader__', None) is not self:
-                _vv and IOLOG.debug(
-                    '%r: %r is submodule of a package we did not load',
-                    self, fullname
-                )
-                return None
-
+            _v and LOG.debug('%r.find_module(%r)', self, fullname)
             # #114: explicitly whitelisted prefixes override any
             # system-installed package.
             if self.whitelist != ['']:
                 if any(fullname.startswith(s) for s in self.whitelist):
                     return self
 
+            pkgname, dot, _ = fullname.rpartition('.')
+            pkg = sys.modules.get(pkgname)
+            if pkgname and getattr(pkg, '__loader__', None) is not self:
+                LOG.debug('%r: %r is submodule of a package we did not load',
+                          self, fullname)
+                return None
+
+            suffix = fullname[len(pkgname+dot):]
+            if pkgname and suffix not in self._present.get(pkgname, ()):
+                _v and LOG.debug('%r: master doesn\'t know %r', self, fullname)
+                return None
+
             try:
                 self.builtin_find_module(fullname)
                 _vv and IOLOG.debug('%r: %r is available locally',

mitogen/master.py

@@ -471,7 +471,7 @@ class ModuleFinder(object):
                 for name in maybe_names
                 if sys.modules.get(name) is not None
                 and not is_stdlib_name(name)
-                and 'six.moves' not in name  # TODO: crap
+                and u'six.moves' not in name  # TODO: crap
             )
         ))