Fix some build issues

- Use %z for size_t format specifier. Why does size_t need its own
  format specifier? it's a different size each platform. This is C;
  portability is job number uh... it's somewhere on the list I know it!
- Fix compiler error with time_t due to the system time_t never getting
  included (C99 says there's no difference between <> and "", thus you
  are including your own header and the system one never gets included -
  retarded? yes. It's C)
- There's some other warnings. I can't really fix them due to a conflict
  you have with src/common/string.h with system string.h. They're
  harmless for now but expect problems later. Again, C(TM).

Basically tl;dr <> and "" have no difference at all, they're merely a
convention (as I found out for myself, but I've always avoided naming
things after system headers as I get confused). Also, C sucks.

Seriously.