This reverts commit 7f8ff2867c.

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")

These options have been deprecated for over a year.

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

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