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/cfitsio/package.py

@@ -14,10 +14,10 @@ class Cfitsio(AutotoolsPackage):
     homepage = 'http://heasarc.gsfc.nasa.gov/fitsio/'
     url      = 'http://heasarc.gsfc.nasa.gov/FTP/software/fitsio/c/cfitsio3450.tar.gz'
 
-    version('3.450', 'f470849bb43561d9a9b1925eeb7f7f0d')
-    version('3.420', '26e5c0dfb85b8d00f536e706305caa13')
-    version('3.410', '8a4a66fcdd816aae41768baa0b025552')
-    version('3.370', 'abebd2d02ba5b0503c633581e3bfa116')
+    version('3.450', sha256='bf6012dbe668ecb22c399c4b7b2814557ee282c74a7d5dc704eb17c30d9fb92e')
+    version('3.420', sha256='6c10aa636118fa12d9a5e2e66f22c6436fb358da2af6dbf7e133c142e2ac16b8')
+    version('3.410', sha256='a556ac7ea1965545dcb4d41cfef8e4915eeb8c0faa1b52f7ff70870f8bb5734c')
+    version('3.370', sha256='092897c6dae4dfe42d91d35a738e45e8236aa3d8f9b3ffc7f0e6545b8319c63a')
 
     variant('bzip2', default=True, description='Enable bzip2 support')
     variant('shared', default=True, description='Build shared libraries')