IBUF, FREE SPACE MANAGEMENT

ibuf_merge_or_delete_for_page(): Declare the user index page latched
for UNIV_SYNC_DEBUG after opening the change buffer cursor. This
should avoid the bogus latching order violation.

ibuf_delete_rec(): Add assertions to the callers, checking that the
mini-transaction was committed when the function returned TRUE. This
is a non-functional change, just clarifying the code.

rb#2136 approved by Kevin Lewis