Invalid (old?) table or database name in logs

Post push patch.

Bug was that a non partitioned table file was not
converted to system_charset, (due to table_name_len was not set).

Also missing DBUG_RETURN.

And Innodb adds quotes after calling the function,
so I added one more mode where explain_filename does not
add quotes. But it still appends the [sub]partition name
as a comment.

Also caught a minor quoting bug, the character '`' was
not quoted in the identifier. (so 'a`b' was quoted as `a`b`
and not `a``b`, this is mulitbyte characters aware.)

sql/mysql_priv.h:
  Bug#32430: 'show innodb status' causes errors
  Invalid (old?) table or database name in logs
  
  Added an unquoted mode
sql/share/errmsg.txt:
  Bug#32430: 'show innodb status' causes errors
  Invalid (old?) table or database name in logs
  
  Removed the quoting of identifier, only leaving the translated word.
sql/sql_table.cc:
  Bug#32430: 'show innodb status' causes errors
  Invalid (old?) table or database name in logs
  
  Fixed quoting of '`'
  Added DBUG_RETURN.
  Corrected table_name_len.
  Added unquoted mode.