aeb with no arg does not always make sense as the correct build

We are working on a project that has two different development
instances (to keep the frontend team from clobbering the backend team
for example) and at first I wanted to make it so the default cook
target would return an error telling you needed to run one of the top
level nodefault targets, but aede/aefinish refused to reconize that a
valid build was performed.   So what I did was make the default target
"polymorphic" based on user name.   The below is the skeleton of the
final cookbook but I would of prefered to have "all" just throw an
error.

manifest=[collect aelpf] [collect aelcf];
src=[match_mask %0%.java [manifest]];

search_list=[split ":" [search_path]];

if [match aryeh [user]] then finalTarget=back;
else
if [match dnixon [user]] then finalTarget=back;
else
if [match bwong [user]] then finalTarget=front;

rm -rf obj;
mkdir obj;

all:  [finalTarget]
        set default;

back: [src]
        set nodefault
{
   ...
}

front: [src]
        set nodefault
{
   ...
}