patch applied (ghc): Add a --supported-languages flag

[Ian Lynagh]

Sun Aug  5 08:33:41 PDT 2007  Ian Lynagh <igloo at earth.li>
  * Add a --supported-languages flag
  Print the list of strings that are accepted in a LANGUAGE pragma,
  or as a -XFoo flag. (No can be prepended to any of the strings).

    M ./compiler/main/DynFlags.hs -1 +4
    M ./compiler/main/Main.hs -17 +28
    M ./docs/users_guide/flags.xml +6
    M ./docs/users_guide/using.xml +12