branches/zip: Correctly identify deleted records when deciding whether to copy BLOB pointers.
branches/zip: Correctly identify deleted records when deciding whether to
copy BLOB pointers.

page_zip_dir_find_free_low(): New function,
split from page_zip_dir_find_free().

Add comments about processing the records in heap_no order.

Fix some typographic errors in comments and improve formatting.

page_zip_decompress(): Initialize (clear) the BLOB pointers in deleted records.

page_zip_clear_rec(): Relocate page_zip_validate() assertions, so that they
will not fail if a record containing BLOB pointers is being deleted.

Note that page_zip_validate() will fail if page_zip_clear_rec() is unable
to clear the record.

flynn1973/mariadb-aix,davidl-zend/zenddbi,natsys/mariadb_10.2,natsys/mariadb_10.2,flynn1973/mariadb-aix,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,flynn1973/mariadb-aix,ollie314/server,ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,davidl-zend/zenddbi,slanterns/server,davidl-zend/zenddbi,flynn1973/mariadb-aix,ollie314/server,davidl-zend/zenddbi,davidl-zend/zenddbi,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,flynn1973/mariadb-aix,ollie314/server,ollie314/server,davidl-zend/zenddbi,flynn1973/mariadb-aix,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,natsys/mariadb_10.2,davidl-zend/zenddbi,ollie314/server,ollie314/server,natsys/mariadb_10.2