Bug#14530242 CRASH / MEMORY CORRUPTION IN FILESORT_BUFFER::GET_RECORD_BUFFER WITH MYISAM

This is a backport of
Bug#12694872 - VALGRIND: 18,816 BYTES IN 196 BLOCKS ARE DEFINITELY LOST
Bug#13340270: assertion table->sort.record_pointers == __null
Bug#14536113 CRASH IN CLOSEFRM (TABLE.CC) OR UNPACK (FIELD.H) ON SUBQUERY WITH MYISAM TABLES

Also:
removed and re-added test files with file-ids from trunk.