(s_mri): New function.
* read.h (s_mri): Declare.
* app.c (scrub_m68k_mri): New static variable.
(mri_pseudo): New static variable.
(do_scrub_begin): Add m68k_mri parameter. Use it rather than
flag_m68k_mri. Initialize scrub_m68k_mri.
(mri_state, mri_last_ch): New static variables.
(struct app_save): Add scrub_m68k_mri, mri_state, and mri_last_ch
fields.
(app_push): Save new fields.
(app_pop): Restore new fields.
(do_scrub_chars): Check scrub_m68k_mri rather than flag_mri_mri.
If TC_M68K, use a trivial state machine to look for occurrences of
the .mri pseudo-op, and change the mode appropriately.
* as.h (do_scrub_begin): Update prototype.
* input-scrub.c (input_scrub_begin): Pass flag_m68k_mri to
do_scrub_begin.
* config/tc-m68k.c (reg_prefix_optional_seen): New static
variable.
(m68k_mri_mode_change): New function.
(md_parse_option): Set reg_prefix_optional_seen.
* config/tc-m68k.h (m68k_mri_mode_change): Declare.
(MRI_MODE_CHANGE): Define.
* doc/as.texinfo: Document .mri pseudo-op.