New DISCOVAR release

A new release (r46399) of DISCOVAR is now available. It contains the following changes:

- More robust SAMtools version checking.
- Improvements to .variant file format.
- MALLOC_PER_THREAD = 1 environment setting no longer mandatory. However setting this may give a significant performance boost.
- Various bug fixes.

Thanks to all the users who have brought these problems to our attention.