(struct buffer): Fields markers and intervals moved out.

(struct buffer): Fields markers and intervals moved out.
(struct buffer_text): Fields markers and intervals moved here.
(BUF_MARKERS, BUF_INTERVALS): New macros.

(struct buffer): Make buffer_file_type field unconditional.

(struct buffer): New field pt_marker.
save_modiff field deleted.
(struct buffer_text): save_modiff field moved here.
(SAVE_MODIFF, BUF_SAVE_MODIFF): New macros.
Use them instead of direct access to save_modiff field.

(struct buffer): New fields begv_marker, zv_marker.

(struct buffer): Make text field be a pointer.
The struct buffer_text field renamed to own_text.
Add fields indirect_to_buffer and size.
Move pt, begv and zv fields here.
(struct buffer_text): Moved from here.
(BEGV, PT, ZV, BEGV_ADDR, PT_ADDR, ZV_ADDR): Corresponding changes.
(BUF_BEGV, BUF_PT, BUF_ZV): Corresponding changes.
(SET_BUF_ZV, SET_BUF_PT, point):