Change 'mysql' client to output XML like the 'mysqldump'

tool does, with the column names as attributes on <field>
elements, instead of trying to use the column name as the
element name. Also fix some encoding issues. (Bug #7811)


client/mysql.cc:
  Quote > and " in XML output, and use <field name="XXX"></field>
  instead of <XXX></XXX>, to make the output more like
  mysqldump --xml and avoid having to turn XXX into a sensible
  element name.

mysql-test/t/client_xml.test

@@ -0,0 +1,18 @@
+# Test of the xml output of the 'mysql' and 'mysqldump' clients -- makes
+# sure that basic encoding issues are handled properly
+create table t1 (
+  `a&b` int,
+  `a<b` int,
+  `a>b` text
+);
+insert into t1 values (1, 2, 'a&b a<b a>b');
+--exec $MYSQL --xml test -e 'select * from t1'
+--exec $MYSQL_DUMP --xml test
+
+--exec $MYSQL --xml test -e 'select count(*) from t1'
+--exec $MYSQL --xml test -e 'select 1 < 2 from dual'
+--exec $MYSQL --xml test -e 'select 1 > 2 from dual'
+--exec $MYSQL --xml test -e 'select 1 & 3 from dual'
+--exec $MYSQL --xml test -e 'select null from dual'
+
+drop table t1;