(regression)

Problem was that partition pruning did not exclude the
last partition if the range was beyond it
(i.e. not using MAXVALUE)

Fix was to not include the last partition if the
partitioning function value was not within the partition
range.

mysql-test/r/partition_innodb.result:
  Bug#51830: Incorrect partition pruning on range partition
  (regression)
  
  Updated result
mysql-test/r/partition_pruning.result:
  Bug#51830: Incorrect partition pruning on range partition
  (regression)
  
  Updated result
mysql-test/t/partition_innodb.test:
  Bug#51830: Incorrect partition pruning on range partition
  (regression)
  
  Added test for pruning in InnoDB, since it does not show
  for MyISAM due to 'Impossible WHERE noticed after reading
  const tables'.
mysql-test/t/partition_pruning.test:
  Bug#51830: Incorrect partition pruning on range partition
  (regression)
  
  Added test
sql/sql_partition.cc:
  Bug#51830: Incorrect partition pruning on range partition
  (regression)
  
  Also increase the partition id if not inside the last partition
  (and no MAXVALUE is defined).
  
  Added comments and DBUG_ASSERT.