If we have lower_case_table_names == 2 (usually on case insensitive file
systems) we sometimes make 'homedir' part of the path sent to the
handler into lowercase. So in this case HEAP engine couldn't properly
find and remove HP_SHARE, what caused the bug.


sql/handler.cc:
  bug #28309 First insert violates UNIQUE constraint - was "memory" table empty?
      
  we don't turn homedirectory part of the path into lowercase
sql/mysql_priv.h:
  bug #28309 First insert violates UNIQUE constraint - was "memory" table empty?
      
  mysql_data_home_len introduced
sql/mysqld.cc:
  bug #28309 First insert violates UNIQUE constraint - was "memory" table empty?
      
  mysql_data_home_len value is set with the mysql_data_home