garbles data if longer than 766 chars.

The problem is that a stored routine returns BLOBs to the previous
caller, BLOBs are shallow-copied (i.e. only pointers to the data are
copied). The fix is to also copy data of BLOBs.


mysql-test/r/sp.result:
  Updated result file.
mysql-test/t/sp.test:
  Added a test case for BUG#18587.
sql/field_conv.cc:
  Do not jump to optimization if the field type is BLOB and
  the destination table requires copying of BLOBs.
sql/item_func.cc:
  Request copying BLOBs for the result table.