[RARSLAVE] Refactoring of PAR2Set

[RARSLAVE] Refactoring of PAR2Set

This patch moves much of the functionality required only by the PAR2Set
class from the global scope into the PAR2Set class itself. It is now much
more careful about only generating sets of data once (where possible).
Also, it is much more careful to re-generate a set of data when it is
possible (and likely) that it has changed.

Fixes: Failure to remove original versions (.1 extension) of repaired
files.

Signed-off-by: Ira W. Snyder <devel@irasnyder.com>