`_zsh_autosuggest_widget_accept()` (&al.) passes this function's return status
on, and ZLE rings the bell if it's >0. Not having an original widget isn't an
error condition, so always returning 0 here should be OK to avoid the bell

Fixes #228

To support older versions of zsh (< 5.0.8).

We were missing the EXTENDED_GLOB option that allows use of `(#m)` flag.

This reverts commit 7f8ff2867c.

This fixes a small issue in src/widgets.zsh which makes it so if you
alias [ to g[ (as is done in prezto if the gnu-utility module is loaded)
autosuggestions would fail.

The documentation for GNU test mentions that -o and -a should be avoided
if possible because it's not very clear. Also, with zsh and [[ -o
actually tests if an option is set, which makes this option even more
confusing.

Now that patch has released

Fixes github issue #271

Maybe this is also a fix for #247, #248 and #258. Supersedes #267.

Testcase:
Using match_prev_cmd strategy and with these lines in history:
echo '1^'
echo '2^'
echo '1^'

type:
echo       (unexpected suggestion echo '1^' instead of echo '2^')
echo '1^1  (wrong suggestion echo '1^1echo '1^')
echo '1^#  (error "bad math expression")

This commit adds the 'emacs-forward-word' widget to the list of partial
accept widgets.

While they are still experimental

[GitHub #219]

Intended to be helpful for folks using bracketed-paste-magic and other
widgets that use `zle -U`.

Depends on patch to ZSH from workers/40702:

  http://www.zsh.org/mla/workers/2017/msg00414.html

Puts in a better fix for #126 and related issues.

There's no need to re-run feature detection or async_start on every
precmd. Just do those once.

Specifically, highlighting breaks if our widgets are wrapped by z-syn-h
widgets.

Should fix #126

So that it doesn't conflict when the file is sourced again

These options have been deprecated for over a year.

It seems like all the zle-* methods are special and shouldn't be
monkeyed with.

Specifically `zle-isearch-update` and friends. Binding that widget
caused `history-incremental-pattern-search` to stop working.

Fixes zsh-users/zsh-syntax-highlighting#387

Based on e702ec4697/async.zsh (L400-L406)

Checks whether `zpty` gives a file descriptor, which was not the case in
older versions of zsh.

Based on a4b2f81c96/async.zsh (L395-L401)

As far as I know, `fc` makes it impossible to tell whether history items
used an actual newline character or the string "\n". Pulling from the
`$history` array gives a more accurate representation of the actual
command that was run.