Better handling of in file templates

`__END__` in the middle of lines should not be recognized as the end of
the ruby script. Ruby only accepts the line just contain `__END__`.
Beginning/tailing whitespaces are not allowed.

Signed-off-by: Simon Rozet <simon@rozet.name>

Author: Yoji Shidara

lib/sinatra/base.rb

@@ -637,7 +637,7 @@ def use_in_file_templates!(file=nil)
         file ||= caller_files.first
 
         begin
-          data = ::IO.read(file).split('__END__')[1]
+          data = ::IO.read(file).split(/^__END__$/)[1]
         rescue
           data = nil
         end

test/templates_test.rb

@@ -87,6 +87,8 @@ def with_default_layout
   end
 end
 
+# __END__ : this is not the real end of the script.
+
 __END__
 
 @@ foo