PT-2016 pt-table-sync and CRC32 columns (#521)

* PT-2016 CRC32 on key

* PT-2016 Added tests

* Removed commented out line

t/pt-table-sync/samples/pt-2016.sql

@@ -0,0 +1,12 @@
+DROP DATABASE IF EXISTS test;
+
+CREATE DATABASE test;
+
+CREATE TABLE test.test2 (
+  col1 INT NOT NULL,
+  col2 TEXT NOT NULL,
+  col3 VARCHAR(5) NOT NULL,
+  UNIQUE KEY (col1, col2(3))
+);
+
+INSERT INTO test.test2 VALUES(1,'aaa','aaa');