A stored procedure involving substrings could crash the server on certain
platforms because of invalid memory reads.
          
During storing the new blob-field value, the cached value's address range
overlapped that of the new field value. This caused problems when the 
cached value storage was reallocated to provide access for a new 
characater set representation. The patch checks the address ranges, and if
they overlap, the new field value is copied to a new storage before it is
converted to the new character set.


mysql-test/r/sp.result:
  Added result set
mysql-test/t/sp.test:
  Added test case
sql/field.cc:
  The source and destination address ranges of a character conversion must not overlap or the 'from' address will be invalidated as the temporary value-
  object is re-allocated to fit the new character set.
sql/field.h:
  Added comments