Merge pull request #1870 from opscode/lcg/digester-singleton

Lcg/digester singleton
Switches to https://supermarket.getchef.com

This modifies knife cookbook site to use supermarket instead of
cookbooks.opscode.com. Additionally, it switches to using HTTPS instead
of HTTP.
Updates spec for supermarket
adding CHANGELOG for pr #1801
Merge pull request #1871 from opscode/lcg/supermarket-urls

Lcg/supermarket urls
Use thread-safe OpenSSL::Digest instead of Digest
add CHANGELOG for pr #1807
Merge pull request #1872 from opscode/lcg/digester

Lcg/digester
Add insert_at to resource_collection
Modify wording in exception
add CHANGELOG for pr#1395
Merge pull request #1873 from opscode/lcg/insert_at

Lcg/insert at
add_env_to_scm_resource
fix: remove oldline and check avail.
set nil by default, add two specs
HOME can overwrite by user with OVERRIDE_HOME
cleanup: remove OVERRIDE_HOME
add md files for PR #1561
initial pass at supporting version constraints in value_for_platform
use Chef::VersionConstraint, not Gem in value_for_platform