Removed buffer overrun bugs.
Removed buffer overrun bugs.

In full debug mode, FastMM4 fills up allocations with extra, known bytes. If these are
modified, it detects that in FreeMem and issues an error. Apparently, some
routines like InternalMultiplyAndAdd16, UncheckedDivModKnuth and InternalShiftLeft
accessed past their buffer and caused either a FastMM4 error or bad results.

rvelthuis/BigNumbers,rvelthuis/BigNumbers