fix for tiff decompression on PlanarConfigContig

Strip sizes as written in tiff StripByteCounts (tiffStripSize)
specify size of compressed data. As I understand, by tiff6 definition,
uncompressed strip size of PlanarConfigContig image with pixel sizes
that naturally align can be calculated as
rowsPerStrip * width * (sum $ tiffBitsPerSample) .
Samples that are not all of equal and power of two size, or that are
less than 8 bits per pixel might be problematic as they might have
row alignment requirements.

As for images that group sample types (PlanarConfigSeparate), I have
currently have no idea.
enable testing on tiff compression test files
Merge pull request #64 from iger/tiff

fix for tiff decompression on PlanarConfigContig