Disallow conflicting use of variables named "password" and "names". If such
  a variable is declared, and "SET ... = ..." is used for them, an error is
  returned; the user must resolve the conflict by either using `var` (indicating
  that the local variable is set) or by renaming the variable.
  This is necessary since setting "password" and "names" are treated as special
  cases by the parser.


mysql-test/r/sp-error.result:
  New test cases for BUG#13510
mysql-test/t/sp-error.test:
  New test cases for BUG#13510
sql/share/errmsg.txt:
  New error message for when certain variable names are use which would be
  parsed the wrong way. (E.g. "password" and "names")
sql/sql_yacc.yy:
  Check if "names" or "password" are used as local variable/parameter, in which
  case "set names" or "set password" will be parsed the wrong way. Give an error
  message instead.