1.3 cleanup: patterns in list comprehensions

[Thomas Johnsson]

Here's another little cleanup item:

Currently, guarded patterns are not allowed i list comprensions.
I see no reason for this restriction, so I propose that we 
allow them.

For example, one cannot write
        [ .... | (a,b)|a==b <- blablabigexpression ]
but one has to write
        [ .... | (a,b) <- blablabigexpression, a==b ]




-- Thomas