[module/forge] (GH-188) Force pmt module installs

In order to allow people to downgrade modules the puppet module tool
must be invoked with `--force`; this commit does the needful.
Merge branch 'defect/1.2.x/gh-188-pmt-module-downgrade' into 1.2.x
Update CHANGELOG and version.rb for 1.2.4
Merge branch '1.2.x' into 1.3.x

Conflicts:
	CHANGELOG.mkd
	lib/r10k/version.rb
Update CHANGELOG.mkd and version.rb for 1.3.4