Bug fix to load_bam_header(). When adding @SQ lines to a header where
the text representation in BAM misses a sequence but the binary one
includes it, we always errored due to incorrectly checking the return code.


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3592 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1
Replacement of the rANS codec. This new one is better optimised, but
also has a smaller encoding of the symbol frequencies and only has 4
way unrolling for the order-1 variant for simplicity (it's the same as
the order-0 one).


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3593 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1