(overlay_heads, overlay_tails): Change to struct sortstrlist.
(overlay_heads_len, overlay_tails_len): Deleted; now part of struct.
(record_overlay_string): New function.
(overlay_strings): Simplify. Use record_overlay_string.
Check for window match in overlays_after loop, not just in
overlays_before.
(last_overlay_modification_hooks_used): Likewise.
(syms_of_buffer): Init last_overlay_modification_hooks.
(add_overlay_mod_hooklist): New function.
(call_overlay_mod_hooks): Call add_overlay_mod_hooklist.
(report_overlay_modification): When AFTER is non-nil,
call the functions recorded in last_overlay_modification_hooks.
unchain that buffer's markers (only) from the common chain.
Don't rekill this buffer's indirect buffers that are dead.
Do nothing if this buffer is already dead.
(Fbuffer_base_buffer): New function.
(syms_of_buffer): defsubr them.
(reset_buffer): Don't alter intervals here.
(Fget_buffer_create): Use BUF_MARKERS. Init BUF_INTERVALS here.
(Fkill_buffer): Use BUF_MARKERS; but don't touch it in indir buf.
Likewise BUF_INTERVALS.
(init_buffer_once): Set up .text and BUF_INTERVALS
in buffer_local_symbols and buffer_defaults.
(Fkill_buffer): Don't free the text in indirect buffer.
When killing a base buffer, kill its indirect buffers first.
(set_buffer_temp): New function.
(reset_buffer_local_variables): Initialize buffer_file_type field.
(Fget_buffer_create): Initialize pt_marker, begv/zv_marker.
(set_buffer_internal): Use and update these markers.
Copy undo_list in and out of the base buffer.
(Fget_buffer_create): Init save_modiff field here.
(reset_buffer): Not here.
(Fbuffer_modified_p): Use BUF_SAVE_MODIFF.
(Fset_buffer_modified_p): Use SAVE_MODIFF.
(Fkill_buffer, list_buffers_1): Use BUF_SAVE_MODIFF.
(Fget_buffer_create): Initialize the size and text fields.
(assoc_ignore_text_properties): New function.
(Fget_buffer): Use assoc_ignore_text_properties.
(Fother_buffer): Take account of frame's buffer predicate.
(call_overlay_mod_hooks): New args AFTER, ARG1, ARG2, ARG3.
Args START, END deleted. Pass each function AFTER, ARG1 and ARG2,
and ARG3 if ARG3 is not nil.
(verify_overlay_modification): New args AFTER, ARG1, ARG2, ARG3.
Pass them to call_overlay_mod_hooks.
