After closer evaluation I am closing this issue from the code completion point of view. Although the parameters cannot
be on the left side of an assignement the user might be typing something else. Consider e.g.

function f(aaa : Integer) : Void {
   aaa
}

The user has typed aaa and can leave as it is or can continue with e.g. + or = but the code completion should not stop
him. Even in case the user has this in the editor

function f(aaa : Integer) : Void {
   var x : Integer = 5;
   aaa| = 10;
}

(the | denotes the caret position) we should keep suggesting aaa since he can easily type 

;<ENTER> x = 

and he is ok with having aaa there --- resulting in 

function f(aaa : Integer) : Void {
   var x : Integer = 5;
   aaa;
   x = 10;
}
So I am closing this issue. If there is some case where our behavoiur is wrong please reopen.

verified in 2008-09-19_02-01-58.zip