import-checker: handle standard modules with arch in the filename

Installations with module names like
/usr/lib/python2.7/lib-dynload/bz2.x86_64-linux-gnu.so occurs in the wild.

Let's just ignore everything after first '.' when guessing the Python module
name.

contrib/import-checker.py

@@ -17,7 +17,7 b' def dotted_name_of_path(path):'
     'zlib'
     """
     parts = path.split('/')
-    parts[-1] = parts[-1][:-3] # remove .py
+    parts[-1] = parts[-1].split('.', 1)[0] # remove .py and .so and .ARCH.so
     if parts[-1].endswith('module'):
         parts[-1] = parts[-1][:-6]
     return '.'.join(parts)