- 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()