FIX: Crash on loading in some cases.
FIX: Possible fix for crashes on new month in the command line server.
REVERT: Previous attempted fix: this caused desyncs and did not fix the crash.

Signed-off-by: James E. Petts <jamespetts@yahoo.com>
FIX: Possible fixes for server crashes
CODE: Better casting
CODE: Rationalise calculation of vehicle resale value to remove floating point arithmeitc
Merge commit 'e28358' (fixes from James's 11.x branch) into emergency-depot-bugfix
Fix floating point use in vehikel_t::calc_restwert() correctly (James's fix still had system floating point math hidden in it)