multiline inserts into partition
Bug#57071: EXTRACT(WEEK from date_col) cannot be
allowed as partitioning function

Renamed function according to reviewers comments.

sql/item.h:
  better name of processor function
sql/item_func.h:
  better name of processor function
sql/item_timefunc.h:
  better name of processor function
sql/sql_partition.cc:
  better name of processor function
  Updated comment.