The test "prefix for system in /" is duplicated in test/prefix.bats.
Both tests are completely identical. This commit removes the
duplication.

It appears that the culprit is this merge from rbenv/master, from 2016:

  cf1beda362

With the current development version of bats, this leads to the
following error when running `make test`:

  Error:
  Duplicate test name(s) in file
  "/home/travis/build/pyenv/pyenv/test/prefix.bats":
  test_prefix_for_system_in_-2f

Note that the development version is what pyenv's Makefile uses. With
the latest release of bats, the duplication only leads to a warning:

  bats warning:
  duplicate test name(s) in /src/test/prefix.bats:
  test_prefix_for_system_in_-2f

* Update help docs to clarify multiple version(s) are allowed

* Tweek version(s) help description

Using `exec -a` caused Python to use $PATH to look up the full program name (for
`sys.executable`), which 314937d then tried to fix by changing $PATH
also for the system version.
This is not necessary anymore when not using the short name with `exec`.

This was rejected upstream
(https://github.com/rbenv/rbenv/pull/1089#issuecomment-394531896), since
it is not a problem with Ruby apparently.

Uses $PYENV_ROOT to check if system version is used.

Fixes https://github.com/pyenv/pyenv/issues/98.
Fixes https://github.com/pyenv/pyenv/issues/789.

This was imported semi-automatically in 0965577, but `ruby -S` is
different from `python -S`.

`ruby -S`: look for the script using PATH environment variable
`python -S`: don't imply 'import site' on initialization

This reverts commit 070e1c859fb2584c3dbe0a6fbe58cbc80938654e, reversing
changes made to 3faeda67bb.

All scripts in libexec/ (excluding pyenv) are called through pyenv,
therefore the shebang lines are not necessary. On some systems this
provides a measurable increase in performance of the shell prompt.

Related to pyenv/pyenv-virtualenv#259

Ref (abs_dirname in bats): https://github.com/sstephenson/bats/pull/224
Ref: https://github.com/rbenv/rbenv/pull/868

Fixes https://github.com/pyenv/pyenv/issues/580

Command `rbenv version-name > .ruby-version` will create an empty `.ruby-version` file
before running `rbenv-version-file`. This causes `rbenv-version-file` to return empty
string which in turn causes `rbenv-version-name` to return `system`.

Ensure size of `.ruby-version` is non-zero as a workaround.

Otherwise `sed` might not be found later in bats/libexec/bats-exec-test,
in case `/usr/bin` gets removed.

Revert back to original quoting style used before previous commit.
Adjust init.bats to reflect changes for successful tests.

https://travis-ci.org/pyenv/pyenv/jobs/215777826

Keeping rbenv-controlled variables to RBENV_* "namespace" helps with
discoverability (and tools like rbenv-env) but also consistency and a
very minor degree of safety/isolation from env impact.

This ensures that OLD_RBENV_VERSION is never exported. This makes the
implementation a little bit more complex, since more logic needs to be
pushed down into eval'd code.

I need to use release date versioning at least for now until preparing
custom version comparator for brew's formula.

`rbenv shell -` allows you to switch to the previously activated ruby
version.  Similar to `cd -` or `git checkout -`.

This tries to implement `rbenv shell -` as proposed in #854.  However,
adding support seemed to break the "shell change version" test.  I'm not
very good at Bash programming, can someone tell me what is wrong with
what I'm doing?  I'd like to add a bit more functionality to this, but
I'm really just cargo cult programming Bash.

Thank you!

fix tests

Use extracted create_hook helper in tests for:

- exec
- hooks
- rehash
- version-name
- version-origin
- which

Spaces in hook path is tested in test/hooks.bats

`default` was made legacy back in 2011 with
5be66da9f4 (the command was renamed from
`rbenv-default` to `rbenv-global`, and so the global file was renamed
from `$RBENV_ROOT/default` to `$RBENV_ROOT/global` (the latter taking
precedence)

`global` was then made legacy about a month later in Sep 2011 when the
preferred filename was changed to `$RBENV_ROOT/version`.

References #730

It doesn't try to chdir into RBENV_ROOT anymore because that might be
a location of an unrelated rbenv install that might have a different
version than the current one that is installed e.g. via a package
manager such as Homebrew.

Now just tries the repo where the source files (`libexec/*`) are
located, and if that isn't a valid rbenv repo, bail out early.

No need for helper function that's gonna be used just once.