Comment 8 for bug 490019

It could be done for past dates, but I don't know where to find a list of GRS longitudes that goes back to before 2010. If such a list was available, say at least one entry per year starting in 1900 or earlier, it may be worth the additional effort beyond Alexander's fix.
This should compute the rot_rotation_offset directly, so that any manual entry in ssystem.ini is overridden. (Wishlist, blueprint?)
G.