Restore codec to profile setting or previous codec upon reset.

Previously, after typing in 'reset' or using 'Clear Scrollback & Reset',
the current codec is lost.

With this patch, typing in 'reset' will cause the codec to stay what
it was before the reset. Using the 'Clear Scrollback & Reset' will
cause the codec to be set to the Profile setting.

This may get backported to 4.6.x


FIXED-IN: 4.7
REVIEW: 101565