bug#9038: 24.0.50; limit expand-abbrev in viper mode state change

[Chong Yidong]

Bob Nnamtrop <bobnnamtrop@gmail.com> writes:

> Changing from viper insert state to vi state (called "changing state"
> below for brevity) causes expand-abbrev to run if abbrev's are turned
> on. This is good but I think the rule for if an abbrev is expanded
> should agree with the rule in self-insert-command when in insert mode.
> Thus "changing state" should only attempt to expand abbrev if and only
> if the previous char has word syntax. This is easily achieved with the
> following patch (against trunk):

Looks reasonable; checked into trunk.  Thanks.