ibuf_page(): Renamed to ibuf_page_low(). Add the parameters file, line
so that the latch diagnostics will be more meaningful.
In debug builds, add the parameter ibool x_latch. When x_latch=FALSE,
do not x-latch the page, but only buffer-fix it for reading the bit.
In UNIV_SYNC_DEBUG, display a message if an insert buffer bitmap page
was already latched. (The message should be displayed in those cases
where the code would have previously failed.)

ibuf_page(): A wrapper macro for ibuf_page_low(). Pass x_latch=TRUE.

ibuf_bitmap_page_get_bits(): Renamed to ibuf_bitmap_page_get_bits_low().
In UNIV_DEBUG, add the parameter latch_mode.
Remove the parameter mtr unless UNIV_DEBUG is defined.

ibuf_bitmap_page_get_bits(): A wrapper macro for
ibuf_bitmap_page_get_bits_low(). Pass latch_type=MTR_MEMO_PAGE_X_FIX.

buf_page_get_gen(): Use ibuf_page_low(x_latch=FALSE) in the debug assertion.
This avoids the possible deadlock.