Limits -Q option (qual_scale) to sensible range 0 to 93.

Fixes wrap-around bug.
Create xfreopen() utility instead of duplicating code
Use kstring instead of asprintf()

This avoids repetitive error handling code, instead assuming kstring
will abort as appropriate.  We also avoid a C99 library function.
Merge asprintf()->kstring rewrite and warning fixes (#161)
Fix buffer overflow

Razip is on life support in this branch, but cherry-pick this from the
standalone branch anyway, in case anyone happens to use this code.
Add split command to samtools

The split command takes BAMs which consist of multiple readgroups
and separates them out into separate files, one for each readgroup.

Signed-off-by: Martin O. Pollard <mp15@sanger.ac.uk>
Add unit test for bam_split.c's count_rg

Add unit test to test count_rg function.

Signed-off-by: Martin O. Pollard <mp15@sanger.ac.uk>