Add a test for Sass::Importers::Filesystem#eql?
Fix exception on Sass::Importers::Filesystem#eql?

Sass::Importers::Filesystem#eql? raised an exception if other is nil or
other doesn't respond to root method.
Merge pull request #1463 from hcatlin/at-root-docs

At-Root Documentation Fix

Closes #1462
Make parent selectors work in selector pseudoclasses.

Closes #1464
Document interpolation in comments.

Closes #1467
Fix a crash for @for loops.

Closes #1468
Merge remote-tracking branch 'nitoyon/filesystem-eql' into stable

Conflicts:
	doc-src/SASS_CHANGELOG.md
Bump VERSION to 3.4.6.
Merge remote-tracking branch 'origin/stable' into stable