Closes #975

It's actually unavailable in the minimal chroots Debian builds our
package on.  That's allowed by POSIX, which specifies ps(1) to be
optional, whereas id(1) —

- is not optional in POSIX
- should exist on every system anyone might run the testsuite on
- has the same length name, so test expectations don't have to be updated
- doesn't take a filename argument (ditto)

That does make the pipeline as a whole somewhat nonsensical
semantically, but it remains just as valid syntactically.

Fixes #942.

Fixes #883.

Closes #937.

Args for proxychains should be f:q => -f file  : -q quiet.

From comments in the same function:
# $precommand_options maps precommand name to values of $flags_with_argument,
# $flags_sans_argument, and flags_solo for that precommand, joined by a
# colon.

Closes #877

Closes #897

Work around <https://github.com/chrisbra/vim-zsh/issues/33>.

* changelog.md: Update links here too.  They have not yet appeared in
    any stable release.

Command used: perl -pi -e 's#http://zsh.sourceforge.net#https://zsh.sourceforge.io#g' **/*(.)

5.8.0.3 was correct until 5.8.1 was released (see the great-grandparent of this
commit, "driver: Bump the in-development is-at-least checks so they return
false on zsh 5.8.1, released yesterday").

5.2 -> 5.3 is simply a typo fix.  zle-line-pre-redraw has been available since then.

Patch by Nuri Jung; extension to cover PCRE by me.  See #747.

Fixes #747.

Fixes #856
Fixes #857

Part of PR #832.

Closes #687, #818.

PR #776 fixed an issue with complex aliases and expansion. However, this change
also introduced a problem with aliases which contain `]` (for example, commonly
seen on macOS: `alias ]=open`), due to using an associative array `seen_alias`,
indexed by the alias name. Due to `"$seen_alias[$arg]"`, it would fail when
`$arg` is expanded to anything containing `]`'. Thus, typing `] /` would result
in:

```
> ] /
(anon):unset:3: seen_alias[]]: invalid parameter name
```

This change fixes the issue by ensuring we properly access keys in the
associative array `seen_alias`.

Older versions of zsh have issues with map keys having special
characters, especially lacking ways to remove such keys. The
issue is described in detail in
https://unix.stackexchange.com/questions/626393/in-zsh-how-do-i-unset-an-arbitrary-associative-array-element.

This fix uses proposal from
[zsh-workers/43269](https://www.zsh.org/mla/workers/2018/msg01073.html),
discovered by Stephane Chazelas, that boils down to avoid removing keys
from the map, and reconstruct the map anew with some keys omitted.

Co-authored-by: @phy1729

Fixes #797.

Fixes #775.

No functional change. Keeps track of how deep we are in expanding nested
aliases for the next commit.

Signed-off-by: Hussaina Begum Nandyala <hexxdump@gmail.com>

Fixes #769

This reverts commit 62c5575848.

The test fails when zsh/parameter is available.