Although this is upstream problem (accidental deletion from Makefile.am), current ace-5.6.5-r1 still has this problem. Patch follows.
Created attachment 169440 [details, diff] ace-missing-refcountable-header.patch This header is referenced by many of the ace's public headers, but never gets installed. Breaks compilation for apps depending on ace library.
Created attachment 169448 [details, diff] ace-missing-headers.patch Found two more missing headers. Now I'm able to compile the application :)
included your patch in ace-5.6.5-r1. Thankyou. the 5.6.6 version does include this patch.