Works in a similar manner to `raises`, but for warnings instead
of exceptions. Also refactored `recwarn.py` so that all the
warning recording and checking use the same core code.
The only remaining 'py.test' references are:
* those referring to the 'py.test' executable
* those in code explicitly testing py.test/pytest module compatibility
* those in old CHANGES documentation
* those in documentation generated based on external data
* those in seemingly unfinished & unmaintained Japanese documentation
Minor stylistic changes and typo corrections made to documentation next to
several applied py.test --> pytest content changes.
Bruno Oliveira
Eric Hunsberger
Anatoly Bubenkov
Pieter Mulder
holger krekel
Jurko Gospodnetić