checksums: use sha256 checksums everywhere

We'd like to use a consistent checksum scheme everywhere so that we can:

    a) incorporate archive checksums into our specs and have a
       consistent hashing algorithm across all specs.

    b) index mirrors with a consistent type of checksum, and not one that
       is dependent on how spack packages are written.

- [x] convert existing md5, sha224, sha512, sha1 checksums to sha256

var/spack/repos/builtin/packages/blasr/package.py

@@ -13,7 +13,7 @@ class Blasr(Package):
     homepage = "https://github.com/PacificBiosciences/blasr/wiki"
     url      = "https://github.com/PacificBiosciences/blasr/archive/5.3.1.tar.gz"
 
-    version('5.3.1', '53c93f499aa4bc10781c87bafc33df2a')
+    version('5.3.1', sha256='ff7da5a03096294572e6c64340354da5c5ee1c86c277e7b899f2c170c1ac4049')
 
     depends_on('ncurses')
     depends_on('hdf5+cxx@1.8.12:1.8.99')