Documentation: Duplicate explicit target name

[adamjstewart]

In the Basic Usage documentation, there are two Environment Modules links. One points to http://modules.sourceforge.net and the other points to http://wiki.tcl.tk/12999. However, Sphinx doesn't like the fact that the target names are duplicated and issues the following warning message:

basic_usage.rst:4: WARNING: Duplicate explicit target name: "environment modules".

This bug was discovered in #1576 by adding documentation testing. It will be fixed in #1576. This issue is being opened to track the problem.

[adamjstewart]

Solution is to convert the named hyperlink references to anonymous hyperlink references:
http://stackoverflow.com/a/14067756/5828163