Backport mkdir_p path fix for Manifest
Merge pull request #561 from johnnyshields/patch-1

Backport mkdir_p path fix for Manifest to 2.x branch
Add changelog for manifest fix
Sprockets 2.12.1
Merge branch '2.x'

Conflicts:
	README.md
	lib/sprockets/manifest.rb
Avoiding FileUtils module for now
Require hike 2.1
Try PathUtils instead
Include PathUtils in Base
Pull in hike's fileutils
Extract stat_tree into PathUtils
Add stat_directory
Test logical path with bower and index
Move logical path into paths concern
Always remove index.js from logical path name
Rename doc fixture
Rework manifest filter compilers
Build asset require tree at bundled asset level
Required paths should not always be dependencies
Remove processor return support for dependency_assets