64bit conversions (including the long ones) are not safe, because not
every number can be converted to the 2^53 JS numbers and pretending to
do so is asking for bugs.
Explicitly use the double type in the Replay menu, because std::time_t
is unspecified and some platforms like Ubuntu yakkety:i386 fail to
build, looking for long.
Double should work for the next 285 million years, becomes consistent
with SavedGame.cpp, is tested by test_ScriptConversions.cpp and doesn't
pretend to cover all 64bit numbers.
Patch By: echotangoecho
Differential Revision: https://code.wildfiregames.com/D205
Refs #3848 D84 D112
This was SVN commit r19367.