Floating point rounding modes: we should restrict them slightly

[Brad Roberts]

Walter Bright wrote:
> Don wrote:
>> We could get close, I think. We could catch all violations in SafeD.
>> Disallow calling core.stdc.fenv functions from inside SafeD modules,
>> and provide an RAII object in std.math for changing the rounding mode.
>>
>> Actually there's probably a few other C functions we want to prohibit
>> in SafeD -- the infamous string functions, for example.
> 
> Yes, all the C functions will have to be gone through and separated.
> strlen() is safe, while strcpy() and printf() are not.

You sure?  Does running beyond the bounds of the array if there's no null
termination count as safe some how? :)