* reduce stale lock TTL to 2 min, check for stale lock before acquiring and each time -- to hold up new shell sessions for as little as possible

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Co-authored-by: Ivan Pozdeev <vano@mail.mipt.ru>

fixes stalling for 60s and failing if some past fault
has resulting in a stale lockfile being present

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Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

Separate the corner-cutting code for `rehash' into a dedicated branch.

Saves some more time (about 100ms for the large fixture)

register_shim() already deduplicates via associative array (bash 4+) or
by checking if a shim already exists (bash 3.2). The sort -u pipe in the make_shims
call is thus redundant -- the dedup happens downstream regardless. Shim
creation is order-independent and idempotent, so sorting has no semantic
effect either.

Saves one subprocess fork during every rehash invocation.

macOS 12 `mktemp' doesn't support `-p`

It's impossible to 100% reliably extract the script argument from the command line for all and unknown Python versions and implementations

This reverts commit 493f036928.

# Conflicts:
#	libexec/pyenv

"hyperfine pyenv-rehash" before on my bash 4.4:

Time (mean ± σ):   172.8 ms ±   8.2 ms [User: 185.0 ms, System: 24.8 ms]
Range (min … max): 164.2 ms … 198.4 ms 15 runs

After:

Time (mean ± σ):   113.8 ms ±   2.8 ms [User: 127.1 ms, System: 26.1 ms]
Range (min … max): 108.0 ms … 117.6 ms 25 runs

Try for that long no matter what the sleep step available is.

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

For now the code is using traditional pseudo locking mechanism
based on `noclobber`.

`PYENV_FILE_ARG` is used here to make use of `abs_dirname` later in
`libexec/pyenv`.

Fixes https://github.com/yyuu/pyenv/issues/404

This is required for the shims to handle `#!/usr/bin/env python3` in a
shebang, just like `python` is handled currently: it will set
`PYENV_DIR` to the root of the invoked script, which is required for a
`.python-version` script to get picked up from there.

This was rejected for rbenv, where it does not make much sense
(https://github.com/sstephenson/rbenv/pull/735).

Ref: https://github.com/yyuu/pyenv/pull/368#issuecomment-102806837

modified rbenv source for Python and renamed to pyenv.