Portability part 1 - C99 printf

printf, sprintf, fprintf etc are now all C99 compliant. All except sprintf, which is now signaled as deprecated. This raises a few warnings about sprintf usage in the build. Some I fix with pull requests that will follow. Some others should be fixed by the respective authors.
This part affects only when TEST_SNPRINTF is set, i.e. we test this implementation versus the system's. Only ```snprintf()``` is needed. I can't remember why I added these commented lines back in April, I was probably testing the various functions myself. I'll amend a commit removing the comments.