MFC r238178, 238624, 238810:

MFC     r238178, 238624, 238810:

Re-merge a couple of changes from NetBSD libedit.

bin/sh has been taught about el_gets setting the count to -1
on error, so now we can partially revert r238173 to reduce
differences with NetBSD's implementation.

Also fix some warnings to be more in sync with NetBSD.

Obtained from:	NetBSD

git-svn-id: svn://svn.freebsd.org/base/stable/8@239590 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f