* Produce right results for conditions that were transformed to "(partitioning_range) AND
(list_of_subpartitioning_ranges)": make each partition id set iterator auto-reset itself
after it has returned all partition ids in the sequence
* Fix "Range mapping" and "Range mapping" partitioning interval analysis functions to
correctly deal with NULL values.
added THD::work_part_info member where we now store modified
partition_info structure.
It allows no solve problem when different parts of the part_info get
into different mem_roots
Also, moved some of the code out of handler.h and into partition specific files for better
separation.
Also, moved some of the C funcs into partition_info as formal C++ methods
