Fix for issue #268: System endiannes and unaligned memory access issues on mips

[azlicic]

Turns out that the issue I reported is mostly contained within htslib.
This patch only fixes two input test files (that is, in case I'm right about tag values being out of range).

[jmarshall]

This patch is incorrect.

In auxiliary fields, SAM can represent arbitrarily large integers (because it is free text) and BAM can represent integers from -2^31 (as type i) to +2^32 - 1 (as type I). So this samtools test case is testing that conversion from SAM to BAM uses type i or type I as appropriate to represent the value present.

(You might not guess this from the SAM spec, which is written more conservatively for the benefit of Java people who don't believe in unsigned...)