Some errors could not be fatal

[leonbloy]

From [email protected] on January 22, 2014 23:18:10

In particular, if an ancillary chunk has some internal problem (this does not include its outer structure: length - but could include crc), the reader should, optionally, omit them.

Original issue: http://code.google.com/p/pngj/issues/detail?id=28

[leonbloy]

As today, one can skip CRC checking by calling PngReader.setCrcCheckDisabled()

But the idea of that method was mainly to speed up a little the reading. It might be useful
to check the CRC but only emit a warning if fails. And to add more lenient strategies for
reading bad structures (eg, no END chunk, etc)