Fix asset tags for files with more than one dot

After the fix done in 39f9f02, there are cases that will not work
correctly. If you have file with "2 extensions", like foo.min.js and you
reference the file without extension, like:

    javascript_include_tag "foo.min"

it will fail because sprockets finds foo.min.js with foo.min argument.

This commit fixes this case and will get the right file even when
referrencing it without extension.

(closes rails#6598)

actionpack/lib/sprockets/helpers/rails_helper.rb

@@ -157,7 +157,9 @@ def rewrite_asset_path(source, dir, options = {})
         def rewrite_extension(source, dir, ext)
           source_ext = File.extname(source)
           if ext && source_ext != ".#{ext}"
-            if !source_ext.empty? && asset_environment[source]
+            asset = asset_environment[source]
+            if !source_ext.empty? && asset &&
+                  asset.pathname.to_s =~ /#{source}\Z/
               source
             else
               "#{source}.#{ext}"

actionpack/test/template/sprockets_helper_test.rb

@@ -257,6 +257,9 @@ def compute_host(source, request, options = {})
     assert_match %r{\A<script src="/assets/xmlhr-[0-9a-f]+.js" type="text/javascript"></script>\Z},
       javascript_include_tag("xmlhr", "xmlhr")
 
+    assert_match %r{\A<script src="/assets/foo.min-[0-9a-f]+.js" type="text/javascript"></script>\Z},
+      javascript_include_tag("foo.min")
+
     @config.assets.compile = true
     @config.assets.debug = true
     assert_match %r{<script src="/javascripts/application.js" type="text/javascript"></script>},
@@ -310,6 +313,9 @@ def compute_host(source, request, options = {})
     assert_match %r{\A<link href="/assets/style-[0-9a-f]+.ext" media="screen" rel="stylesheet" type="text/css" />\Z},
       stylesheet_link_tag("style.ext")
 
+    assert_match %r{\A<link href="/assets/style.min-[0-9a-f]+.css" media="screen" rel="stylesheet" type="text/css" />\Z},
+      stylesheet_link_tag("style.min")
+
     @config.assets.compile = true
     @config.assets.debug = true
     assert_match %r{<link href="/stylesheets/application.css" media="screen" rel="stylesheet" type="text/css" />},