patch applied (ghc): Fixed remaining warning in coreSyn/MkExternalCore

[Tim Chevalier]

Wed Mar 19 11:25:21 PDT 2008  Tim Chevalier <chevalier at alum.wellesley.edu>
  * Fixed remaining warning in coreSyn/MkExternalCore
  
  There was a (suppressed) warning about an incomplete pattern match in make_alt. This was because the DEFAULT alt never has variable bindings. I thought it would be better to check that case and panic if it happens than to have an incomplete pattern. It's still not great, but at least now we don't have to suppress any warnings in this file.

    M ./compiler/coreSyn/MkExternalCore.lhs -9 +7