closer to branches/zip.

ibuf_size_update(): Add const qualifier to the parameter "root".
Remove #ifdef UNIV_SYNC_DEBUG around ut_ad(mutex_own()).

ibuf_page(): Use the variable name local_mtr instead of mtr_local, to
be more like existing functions.  Eliminate the flag use_local_mtr.

ibuf_get_merge_page_nos(): Restore an "if (...) break; else if" to
"if (...) break; if" as in branches/zip.

ibuf_dummy_index_create(), ibuf_dummy_index_add_col(),
ibuf_contract_ext(), ibuf_insert_low(): Revert to the formatting of
branches/zip.