- Introduced val_int_endpoint() function which converts between func 
  argument intervals and func value intervals for monotonic functions.
- Made partition interval analyzer use part_expr->val_int_endpoint()
  to check if the edge values should be included.


mysql-test/r/partition_pruning.result:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Testcase
mysql-test/t/partition_pruning.test:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Testcase
sql/item.cc:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Added Item_field::val_int_endpoint() implementation
sql/item.h:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Added Item::val_int_endpoint() which converts intervals from argument
    space to function value space for unary monotonic functions.
sql/item_timefunc.cc:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Added val_int_endpoint() for TO_DAYS and YEAR functions.
sql/item_timefunc.h:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Added val_int_endpoint() for TO_DAYS and YEAR functions.
sql/partition_info.h:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Removed partition_info::range_analysis_include_bounds as it is no longer 
    needed.
sql/sql_partition.cc:
  BUG#27927: Partition pruning not optimal with TO_DAYS and YEAR functions
  - Make partition interval analyzer use part_expr->val_int_endpoint() to 
    check if the edge values should be included.