Added test cases for bug #7914.
sql_select.cc:
  Fixed bug #7914: rollup over expresssions such as sum(a)+1.


sql/sql_select.cc:
  Fixed bug #7914: rollup over expresssions such as sum(a)+1.
mysql-test/t/olap.test:
  Added test cases for bug #7914.
mysql-test/r/olap.result:
  Added test cases for bug #7914.