Update the samtools package to support v1.3.1, which
- now uses configure script; and
- now depends on external htslib package.
The dependency on mpc seems to have been bogus, it's never linked in,
nor is it mentioned in the source tree. I *do* have a version in
/usr/lib64, but ldd does not sure it being linked in either....
By depending on 'ncurses' I can do away with the need for the patch.
Package repositories now look like this:
top-level-dir/
repo.yaml
packages/
libelf/
package.py
mpich/
package.py
...
This leaves room at the top level for additional metadata, source,
per-repo configs, indexes, etc., and it makes it easy to see that
something is a spack repo (just look for repo.yaml and packages).
