A lot of small fixes and new test cases.

client/mysqlbinlog.cc:
  Cast removed
client/mysqltest.cc:
  Added missing DBUG_RETURN
include/my_pthread.h:
  set_timespec_time_nsec() now only takes one argument
mysql-test/t/date_formats.test:
  Remove --disable_ps_protocl as now also ps supports microseconds
mysys/my_uuid.c:
  Changed to use my_interval_timer() instead of my_getsystime()
mysys/waiting_threads.c:
  Changed to use my_hrtime()
sql/field.h:
  Added bool special_const_compare() for fields that may convert values before compare (like year)
sql/field_conv.cc:
  Added test to get optimal copying of identical temporal values.
sql/item.cc:
  Return that item_int is equal if it's positive, even if unsigned flag is different.
  Fixed Item_cache_str::save_in_field() to have identical null check as other similar functions
  Added proper NULL check to Item_cache_int::save_in_field()
sql/item_cmpfunc.cc:
  Don't call convert_constant_item() if there is nothing that is worth converting.
  Simplified test when years should be converted
sql/item_sum.cc:
  Mark cache values in Item_sum_hybrid as not constants to ensure they are not replaced by other cache values in compare_datetime()
sql/item_timefunc.cc:
  Changed sec_to_time() to take a my_decimal argument to ensure we don't loose any sub seconds.
  Added Item_temporal_func::get_time() (This simplifies some things)
sql/mysql_priv.h:
  Added Lazy_string_decimal()
sql/mysqld.cc:
  Added my_decimal constants max_seconds_for_time_type, time_second_part_factor
sql/table.cc:
  Changed expr_arena to be of type CONVENTIONAL_EXECUTION to ensure that we don't loose any items that are created by fix_fields()
sql/tztime.cc:
  TIME_to_gmt_sec() now sets *in_dst_time_gap in case of errors
  This is needed to be able to detect if timestamp is 0
storage/maria/lockman.c:
  Changed from my_getsystime() to set_timespec_time_nsec()
storage/maria/ma_loghandler.c:
  Changed from my_getsystime() to my_hrtime()
storage/maria/ma_recovery.c:
  Changed from my_getsystime() to mmicrosecond_interval_timer()
storage/maria/unittest/trnman-t.c:
  Changed from my_getsystime() to mmicrosecond_interval_timer()
storage/xtradb/handler/ha_innodb.cc:
  Added support for new time,datetime and timestamp
unittest/mysys/thr_template.c:
  my_getsystime() -> my_interval_timer()
unittest/mysys/waiting_threads-t.c:
  my_getsystime() -> my_interval_timer()