Write an additional warning message to the server log, 
explaining why a sort operation is aborted.

The output in mysqld.err will look something like:
110127 15:07:54 [ERROR] mysqld: Sort aborted: Out of memory (Needed 24 bytes)
110127 15:07:54 [ERROR] mysqld: Out of sort memory, consider increasing server sort buffer size
110127 15:07:54 [ERROR] mysqld: Sort aborted: Out of sort memory, consider increasing server sort buffer size
110127 15:07:54 [ERROR] mysqld: Sort aborted: Incorrect number of arguments for FUNCTION test.f1; expected 0, got 1

If --log-warn=2 is enabled, we output information about host/user/query as well.


include/my_sys.h:
  Update comment for ME_NOREFRESH
mysql-test/include/mtr_warnings.sql:
  Remove global filtering of "Out of sort memory", let each individual test set it instead.
mysql-test/r/filesort_debug.result:
  New test case.
mysql-test/r/order_by.result:
  Ignore "Out of memory" for this test.
mysql-test/t/filesort_debug.test:
  New test case.
mysql-test/t/order_by.test:
  Ignore "Out of memory" for this test.
sql/filesort.cc:
  Output an explanation using the error message from the THD Diagnostics_area.
sql/protocol.cc:
  Do not DBUG_RETURN(function_call_with DBUG_RETURN)
  as it messes up the call stack in the debug output.
sql/share/errmsg-utf8.txt:
  Change error message for "Out of sort memory"
sql/unireg.h:
  Remove unused/confusing ERRMAPP macro.