When creating histogram statistics, the server needs an estimate of how may
rows there are in the table it is building a histogram for. This estimate
will help the server decide on whether to use sampling or not. However, the
estimate is for instance not updated by insert or delete statements, so
after inserting/deleting a lot of rows the estimate may be way off. This in
turn may cause the server not to use sampling when building histograms when
in fact it should.

This patch makes the histogram creation process ask for the number of
rows in the table so that it can make a better guess on whether to use
sampling or not.

Change-Id: I20b6e55660f2fa36a932c86e6e781ac8bcd4b20f