Fix SVN downloads of versioned formula by munging directory names

Library/Homebrew/download_strategy.rb

@@ -665,6 +665,10 @@ class SubversionDownloadStrategy < VCSDownloadStrategy
     @url = @url.sub("svn+http://", "")
   end
 
+  def cache_filename
+    Resource.safe_download_name("#{name}--#{cache_tag}")
+  end
+
   def fetch
     clear_cache unless @url.chomp("/") == repo_url || quiet_system("svn", "switch", @url, cached_location)
     super

Library/Homebrew/resource.rb

@@ -66,8 +66,18 @@ class Resource
     name.tr("/", "-")
   end
 
+  def self.safe_download_name(str)
+    # "@" is a special character for Subversion. Keep it out of the cache dir name.
+    str.gsub("@", "-AT-")
+  end
+
   def download_name
-    name.nil? ? owner.name : "#{owner.name}--#{escaped_name}"
+    raw_name = if name
+      "#{owner.name}--#{escaped_name}"
+    else
+      owner.name
+    end
+    Resource.safe_download_name(raw_name)
   end
 
   def cached_download