Tests: repeating input files

[mgorny]

The input files in dcparser and dcserialize seem to be repeating:

$ duff -r .
2 files in cluster 1 (1920 bytes, digest 72a122ca9485ecd2b68350f14733daf36f7cbde4)
./dcserialize/andersen_brzydkie_kaczatko.xml
./dcparser/andersen_brzydkie_kaczatko.xml
2 files in cluster 2 (2318 bytes, digest 7b015ab76c72078d66f68b170b7549b346c7e3e8)
./dcserialize/kochanowski_piesn7.xml
./dcparser/kochanowski_piesn7.xml
2 files in cluster 3 (2254 bytes, digest 2b2d21a2a8c01504c623430157379f276d95dbbf)
./dcserialize/mickiewicz_rybka.xml
./dcparser/mickiewicz_rybka.xml
2 files in cluster 4 (1943 bytes, digest 914b998f397f5b76bed525c8a13bfd9ddc27e993)
./dcserialize/sofokles_antygona.xml
./dcparser/sofokles_antygona.xml
2 files in cluster 5 (1799 bytes, digest e0c5556f9264d1357ee94ab4094f9ba60341e629)
./dcserialize/biedrzycki_akslop.xml
./dcparser/biedrzycki_akslop.xml

I think the input files should be moved to a common directory where they could be easily used by all the tests. I want to implement tests for .fb2 and I'd really prefer reusing the existing input rather than introducing a new files or using another format name in input path.