Fix date_Increment when i_divider_den > 1

Fix date_Increment when i_divider_den > 1

Previously, calling date_Increment(d,1) with divider_den > 1 would cause:
 - Uncorrectable rounding error due to ordering of / followed by *
 - If i_divider_num / i_divider_den is not integral, a remainder is
   accumulated, but not divided by i_divider_num when added to date.
 => Both cases are evident with num=30000, den=1001.

This fixes both issues.

Signed-off-by: David Flynn <davidf@rd.bbc.co.uk>