Multiple Extensions

Hackers,

I’m preparing a new release of pgTAP, and have started breaking it down into smaller extensions. I’ve been planning to
havethem all in one distribution file for now, but it seems that one cannot specify multiple extension names in the
EXTENSIONvariable. In my Makefile, I have 
   EXTENSION    = pgtap pgtap-core pgtap-schema

But having more than the one, I get:
   > make   grep: pgtap: No such file or directory   grep: pgtap-core: No such file or directory   grep: pgtap: No such
fileor directory   grep: pgtap-core: No such file or directory   grep: pgtap: No such file or directory   grep:
pgtap-core:No such file or directory   Makefile:79: *** multiple target patterns.  Stop. 

So is that not supported? If not, why not?

Thanks,

David