Fix in optparse definition
Interleaved mode in sample_seqs for paired reads
Sample SFF file using paired sampling.

$ python /mnt/galaxy/galaxy-central/tools/sample_seqs/sample_seqs.py -f sff -i test-data/MID4_GLZRM4E04_rnd30_frclip.sff -o test-data/MID4_GLZRM4E04_rnd30_frclip.pair_sample_N5.sff -n 5 --interleaved
Sampling every 5th sequence
Selected 3 pairs

Note that you probably would never use an SFF file to store interleaved
paired reads, but just in case, testing this route through the code.
Test paired sampling on FASTQ
Test paired FASTA sampling

$ tools/sample_seqs/sample_seqs.py -i test-data/get_orf_input.Suis_ORF.prot.fasta -f fasta -o test-data/get_orf_input.Suis_ORF.prot.pair_sample_N100.fasta -n 100  --interleaved
Sampling every 100th sequence
Selected 15 pairs