Generalize formula_installer dependency resolution

Use `Formula.factory dep.path` instead of `Formula.factory dep.name` so that
non-standard dependencies specified as URLs or paths can be handled properly.

Library/Homebrew/formula_installer.rb

@@ -35,7 +35,7 @@ class FormulaInstaller
               # Re-create the formula object so that args like `--HEAD` won't
               # affect properties like the installation prefix. Also need to
               # re-check installed status as the Formula may have changed.
-              dep = Formula.factory dep.name
+              dep = Formula.factory dep.path
               install_dependency dep unless dep.installed?
             end
           end