The `activate` script does't export the variables of `_OLD_VIRTUAL_*`,
most the deactivation code needed to be moved to `sh-deactivate`.

This makes sure that $VIRTUAL_ENV is handled already in other precmd
functions, especially your prompt.

find proper source version from pyenv if the given executable is only
basename or is a shim script.

https://www.python.org/dev/peps/pep-0370/

- fixes `ps` command to lookup parent process
 - adds `assert_output_contains_not` test helper

Ref: https://github.com/yyuu/pyenv/issues/373

It will be done by `get-pip.py` and we don't have to do anything explicitly.

First release after my son's birth....

This fixes displaying the note, in case "init" has been run manually
and/or the init is not in the expected place.

It removes the unnecessary calls to "grep".

pyenv-virtualenv-init will look at `$PYENV_SHELL` now, too.

Tests have been adjusted/fixed.

When the current pyenv environment is not a virtualenv, this line
exits with a return code of 1. This is annoying for those of us
who report the last return code in our own PROMPT_COMMAND, so
ignore the output of `pyenv activate` if we're not currently using
a virtualenv.

This makes it possible to use `eval "$(pyenv virtualenv-init -)"` from a
function.

"(any command)" is not supported in test in fish, we have to set a
variable and then use that

The situation is when in a directory containing python binary,
`pyenv prefix' will return empty (caused by `pyenv which' returning
"./python"). This change adds quotes for `test', otherwise `test' will
warn about missing argument.

Install script of setuptools-6.1/pip-1.5.6 will create those links if needed

While this could work in general, it fails in the end, because
whitespace is not allowed/supported in the shebang line with the
scripts in the created virtualenv.