Aliases now respect the 'source' config

Alias markdown files were being generated in the current directory
instead of the directory defined by the "source" configuration option.

lib/jekyll-import/importers/drupal_common.rb

@@ -68,6 +68,7 @@ def process(options)
           src_dir = conf["source"]
 
           dirs = {
+            :_aliases => src_dir,
             :_posts   => File.join(src_dir, "_posts").to_s,
             :_drafts  => File.join(src_dir, "_drafts").to_s,
             :_layouts => Jekyll.sanitized_path(src_dir, conf["layouts_dir"].to_s),
@@ -141,12 +142,12 @@ def process(options)
               end
 
               partition = url_alias[:alias].rpartition("/")
-              dir = ""
+              dir = "#{dirs[:_aliases]}/"
               file = partition.last
 
               if partition.first.length.positive?
-                dir = "#{partition.first}/"
-                FileUtils.mkdir_p partition.first
+                dir = "#{dir}#{partition.first}/"
+                FileUtils.mkdir_p dir
               end
 
               File.open("#{dir}#{file}.md", "w") do |f|