[docs] [issue18757] Fix internal references for concurrent modules

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Here is updated patch. Thank Ezio for found errors.

----------
Added file: http://bugs.python.org/file31328/refs.concurrect.diff

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18757>
_______________________________________