Fix reciprocal of a complex number with zero imaginary part.

[gagern]

The reciprocal function is broken when applied to a complex number with zero imaginary part. The code path forgot to use a namespace for the result, and also forgot to include the imaginary part of the result. I added a suitable test case to the documentation to check for this. The missing namespace was found by jshint, the missing imaginary part then exposed by the unit test I had added.