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/xsetpointer/package.py

@@ -12,7 +12,7 @@ class Xsetpointer(AutotoolsPackage):
     homepage = "http://cgit.freedesktop.org/xorg/app/xsetpointer"
     url      = "https://www.x.org/archive/individual/app/xsetpointer-1.0.1.tar.gz"
 
-    version('1.0.1', 'bb206b6875f2428c2281e1165b6c7f88')
+    version('1.0.1', sha256='54be93b20fd6f1deac67246d6e214a60b02dcfbf05295e43751f7a04edb986ac')
 
     depends_on('libxi')
     depends_on('libx11')