Permit unexpanded macros to slip through spec tag sanity checks (RhBug:547997)

Permit unexpanded macros to slip through spec tag sanity checks (RhBug:547997)
- For now, let %{} characters through our valid character set checks
  on specs. This isn't right really, but unexpanded, unrelated macros
  in spec can now cause failure to parse out buildrequires which would
  allow those macros to be expanded. This needs a better fix.