Dont waste time with argi for rpmfc file class indexes

Dont waste time with argi for rpmfc file class indexes

- argiAdd() isn't as costly as argvAdd(), but it still involves unnecessary
  reallocation on every addition as the number of files is predetermined,
  and each file has an associated class index.
- Additionally fixes a mostly harmless glitch introduced in commit
  65e616cc9fdd00f523939088fab1070021b9f742: the pool id's are one larger
  than the indexes we store in headers, take this into account in the
  debug output.