Lifted the limitation that hash join could not be used over 
varchar fields with non-binary collation.

- Merge with 5.3-main

set thd->password appropriately also for cases when a user was not found.

- Fixes for the second fix: take into account case where we don't need to save/restore the scan.

Switch from "Disable identical key handling optimization when
  IndexConditionPushdown is used" approach
To 
 an approach where we save/restore index tuple and so can use index condition pushdown.

mwl#21.

It was missing from EXTRA_DIST in Makefile.am.

 - Address Monty's review feedback, portion 3

- Address Monty's review feedback, portion 2

- Better warnings

Analysis:
The assert failed because st_select_lex::print() was called for subqueries
as follows:

Item_subselect::print() ->
  subselect_single_select_engine::print() -> st_select_lex::print()

It was Item_subselect::fix_fields() that set the thd by calling set_thd(),
so when this print() was called before fix_fields(), subselect_engine::thd
was NULL.

Solution:
The patch makes all constructors of all subselect_engine classes to take
a THD parameter. The default subselect_single_select_engine engine is created
early during parse time, in the Item_subselect::init call, so we pass the
correct THD object already at this point.

- Address review feedback: change return type of RANGE_SEQ_IF::next()

(Includes patch for overrun detected by valgrind thanks to previous my_alloca() -> my_malloc() patch)

mysys/thr_lock.c:
  Fixed typo that caused compile failure

- This allows us to detect missing my_afree() calls and also find overruns (when running with valgrind) to alloca() areas.
- Added missing my_afree() calls
- Fixed wrong call to my_afree()


include/my_sys.h:
  When compiling with valgrind, change my_alloca() to use my_malloc()
mysql-test/suite/innodb/t/innodb_bug57255.test:
  Speed up taste case (patch from Stewart Smith)
mysql-test/suite/innodb_plugin/t/innodb_bug57255.test:
  Speed up taste case (patch from Stewart Smith)
sql/ha_partition.cc:
  Removed casts from my_afree()
sql/opt_range.cc:
  Add missing my_afree() calls.
storage/maria/ma_rt_split.c:
  Fixed wrong parameter to my_afree()

pointers.

storage/maria/ma_check.c:
  Allocate also memory for nodflag and transid's
storage/maria/ma_write.c:
  Allow nodflag and transid as part of key.
  (This has nothing to do with the bug report, but it's a safer check).
storage/maria/maria_def.h:
  Define MARIA_MAX_POINTER_LENGTH (length of pointer to node)
  Added node pointer length to MARIA_INDEX_OVERHEAD_SIZE, as this is part of the key.
  (Safety fix)

Made archive.test a bit more safe



mysql-test/r/archive.result:
  Added removal of files to make rerun of failed test work
mysql-test/t/archive.test:
  Added removal of files to make rerun of failed test work
mysys/thr_lock.c:
  Better warning message if lock test fails

Also:
Changed the value of TIME_FOR_COMPARE_ROWID to make it the same as for MWL 21.
Changed some queries in range_vs_index_merge.test to make them generate
the same plans as earlier.

- Make Mrr_ordered_index_reader() save the rowid across scan interruptions

Also
- Fix compiler warning for setup_buffer_sizes()
- Add commented key_copy/key_restore for better handling of a similar issue
  with index record being destroyed by scan interruption (which causes 
  incorrect evaluation of pushed index condition later on).