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/callpath/package.py

@@ -13,9 +13,9 @@ class Callpath(CMakePackage):
     homepage = "https://github.com/llnl/callpath"
     url      = "https://github.com/llnl/callpath/archive/v1.0.1.tar.gz"
 
-    version('1.0.4', '39d2e06bfa316dec1085b874092e4b08')
-    version('1.0.2', 'b1994d5ee7c7db9d27586fc2dcf8f373')
-    version('1.0.1', '0047983d2a52c5c335f8ba7f5bab2325')
+    version('1.0.4', sha256='4949974d60f18bb34e44e5a4e60032c39624dde5c3f16d557b3a6845eead4e2e')
+    version('1.0.2', sha256='cbe42bba8b9dda259dcbe7e16ebd7ecd005eabf7e9ccf169535b03110df75c84')
+    version('1.0.1', sha256='9bd9723126f80d0b518c28e5298ad0fa8d8dbc6a3f03fee5ae5449cf4c9a550f')
 
     depends_on('elf', type='link')
     depends_on('libdwarf')