libxcmd: use emacs mode for command history editing

libxcmd: use emacs mode for command history editing

Prior to xfsprogs 5.7.0, we built xfsprogs with libreadline support by
default.  In its default configuration, that library interpreted various
keystrokes in a direct manner (e.g. backspace deletes the character to
the left of the cursor), which seems consistent with how emacs behaves.

However, libeditline's default keybindings are consistent with vim,
which means that suddenly users are presented with not the same line
editing interface that they had before.  Since libeditline is
configurable (put "bind -v" in editrc if you really want vim mode),
let's put things back the way they were.  At least as much as we can.

Fixes: bbe12eb9 ("xfsprogs: remove libreadline support")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>