When using python's built-in venv activaton script
warnings are printed when hashing is disabled in
bash or zsh, like;
`bash: hash: hashing disabled`
This output is not really useful to the end-user and has
been disabled in `virtualenv` for long.
This commit is based on:
28e85bcd80
Before, running deactivate from a bash shell configured to treat undefined variables as errors (`set -u`) would produce a warning:
```
$ python3 -m venv test
$ source test/bin/activate
(test) $ deactivate
-bash: $1: unbound variable
```
The activation scripts generated by venv were inconsistent in how they changed the shell's prompt. Some used `__VENV_PROMPT__` exclusively, some used `__VENV_PROMPT__` if it was set even though by default `__VENV_PROMPT__` is always set and the fallback matched the default, and one ignored `__VENV_PROMPT__` and used `__VENV_NAME__` instead (and even used a differing format to the default prompt). This change now has all activation scripts use `__VENV_PROMPT__` only and relies on the fact that venv sets that value by default.
The color of the customization is also now set in fish to the blue from the Python logo for as hex color support is built into that shell (much like PowerShell where the built-in green color is used).
Dima
Daniel Abrahamsson
Brett Cannon
Sorin Sbarnea
Vinay Sajip