Now ESCAPE in LIKE will accept not only string literal but constant 
delimited expression.


mysql-test/r/func_like.result:
  Added test for bug# 4200 "Parse error on LIKE ESCAPE with parameter binding"
mysql-test/t/func_like.test:
  Added test for bug# 4200 "Parse error on LIKE ESCAPE with parameter binding"
sql/item_cmpfunc.cc:
  Added support for accepting of constant delimited expression as ESCAPE argument to
  Item_func_like.
sql/item_cmpfunc.h:
  Now ESCAPE clause in LIKE will accept not only string literal but constant delimited 
  expression. Thus added member to Item_func_like for storing Item corresponding to this
  expression and changed third argument of cons to be Item* instead of char*.
sql/sql_help.cc:
  Item_func_like now accepts Item* as third argument.
sql/sql_yacc.yy:
  Now ESCAPE clause of LIKE accepts not only string literal but constant delimited expression
  (the most important case is prepared statement parameter of course).