Invalidate region caches only if buffer text is going to be changed.

Invalidate region caches only if buffer text is going to be changed.
* lisp.h (modify_region_1): Remove 3rd arg and rename to...
(modify_text): ...new prototype.
(prepare_to_modify_buffer_1): New prototype.
* textprop.c (modify_region): Rename to...
(modify_text_properties): ...new function.
(add_text_properties_1, set_text_properties, Fremove_text_properties)
(Fremove_list_of_text_properties): Adjust users.
* insdel.c (modify_region_1): Remove 3rd arg and reimplement as...
(modify_text): ...new function.
(prepare_to_modify_buffer): Reimplement mostly as a wrapper for...
(prepare_to_modify_buffer_1): ...new function.
* casefiddle.c (casify_region):
* editfns.c (Fsubst_char_in_region, Ftranslate_region_internal)
(Ftranspose_regions): Use modify_text.