Replace remaining 4 calls to sprintf with snprintf

[seanm]

After #3421 there are still 4 uses of sprintf that should be replaced with snprintf.

[kbevers]

Could you point out where they are and why they are complicated to get rid of?

[seanm]

All 4 are in rtodms. The complication is:

1. rtodms takes a buffer (s), but not its size. The function signature should probably change to take the size of the s buffer too.
2. s gets aliased to ss
3. there is pointer arithmetic on ss
4. ss is what's passed to sprintf