for more accurate Valgrind debugging.
univ.i: Introduce UNIV_DEBUG_VALGRIND, UNIV_MEM_VALID, and UNIV_MEM_INVALID.
buf_LRU_block_free_non_file_page(): Invalidate the buffer frame
with UNIV_MEM_INVALID().
buf_LRU_get_free_block(): Declare the buffer frame valid
with UNIV_MEM_VALID().
Other memory is allocated and deallocated via malloc() and free(),
which are already overridden by Valgrind. Without the added
instrumentation, accesses to free pages in the buffer pool cannot
be caught.
The diagnostics could probably be improved further by declaring all
non-latched buffer frames invalid.
buf_flush_init_for_writing(): Improve the diagnostics and make the
condition for skipping pages accurate.
univ.i: Introduce UNIV_ZIP_DEBUG for enabling some page_zip_validate() tests.
page0zip.h, page0zip.c: Define and use page_zip_validate() in
page_zip_compress() and page_zip_write() if UNIV_ZIP_DEBUG or UNIV_DEBUG
is defined.
