use the original stream.
- avoid resetting capture FDs/sys.stdout for each test by keeping capturing
always turned on and looking at snapshotted capturing data during runtest
and collection phases.
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.
```
timeit result for 10000 iterations of expanding '/d' (lowered the count in the code afterwards)
# 2.7.5 3.3.2
# FilesCompleter 75.1109 69.2116
# FastFilesCompleter 0.7383 1.0760
```
- does not display prefix dir (like bash, not like compgen), py.test /usr/<TAB> does not show /usr/bin/ but bin/