Assign syntax to a file without an extension in Sublime Text 2

sublimetext2

Solution

Menu: Preferences -> Browser Packages

Then open the file Ruby\Ruby.tmLanguage

Look up for this block:

<array>
    <string>rb</string>
    <string>rbx</string>
    <string>rjs</string>
    <string>Rakefile</string>
    <string>rake</string>
    <string>cgi</string>
    <string>fcgi</string>
    <string>gemspec</string>
    <string>irbrc</string>
    <string>capfile</string>
    <string>Gemfile</string>
</array>

Add the new entry:

    <string>Guardfile</string>

Problem

I have a file `Guardfile` in my rails project, but appears just in plain text, so each time is opened it must be assigned the ruby syntax to display it correctly. I cannot use `Open all with current extension as...` because it doesn't have an extension, but I suppose I could assign a specific syntax to a file without an extension because files like `Gemfile`, `Capfile` or `Rakefile` are displaying correctly. How can I achieve this?

Original source