Fix 'make dist' on systems without gcrypt

Set DIST_SUBDIRS and include all subdirectories in
tests/exslt/Makefile.am.

tests/exslt/Makefile.am

 ## Process this file with automake to produce Makefile.in
 
 SUBDIRS=common functions math saxon sets strings dynamic date $(CRYPTO_TESTDIR)
+DIST_SUBDIRS = common functions math saxon sets strings dynamic date crypto
 
 test tests:
 	@(cur=`pwd` ; for dir in $(SUBDIRS) ; do cd $$dir ; $(MAKE) CHECKER='$(CHECKER)' tests ; cd $$cur ; done)