(GH-535) Use 32bit checksum/checksumtype when force x86

Previously when forcing x86, packages that specify a checksum will fail
based on a bad checksum. This ensures that when force x86 is specified, the
package will be checked with the 32bit checksum and checksumtype.
(doc) add documentation surrounding checksum & checksumtype
0.9.8.28-alpha2
Merge branch 'stable'

* stable:
  0.9.8.28-alpha2
  (doc) add documentation surrounding checksum & checksumtype
  (GH-535) Use 32bit checksum/checksumtype when force x86