Add imctrl and imkey options, inspired by cannactrl and fepkey options in
nvi-m17n by itojun.

If imctrl option is set, input method is controlled by using escape
sequences compatible to Tera Term an

Add imctrl and imkey options, inspired by cannactrl and fepkey options in
nvi-m17n by itojun.

If imctrl option is set, input method is controlled by using escape
sequences compatible to Tera Term and RLogin. The state of input method in
commands specified by imkey option is saved and restored automatically.
Input method is then deactivated on returning to command mode.

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- replace CIRCLEQ with TAILQ
- fix open-coded LIST code
- fix destroy screen bug (was not removed from list)

Apply our local changes.

Import nvi-1.81.6 + HEAD-2013-11-20 from git://repo.or.cz/nvi.git