build: Add missing test files to the distribution.

* Makefile.am (EXTRA_DIST): Add ‘tests/common.scm’ and ‘tests/mail.sh’.
* tests/database.scm (mailer): Use ‘search-path’ to locate ‘mail.sh’
relative to $top_srcdir.

Makefile.am

@@ -211,7 +211,9 @@ EXTRA_DIST =					\
   examples/cuirass.scm				\
   examples/random.scm				\
   examples/random-manifest.scm			\
-  $(TESTS)
+  $(TESTS)					\
+  tests/common.scm				\
+  tests/mail.sh
 
 dist-hook:
 	$(AM_V_GEN)echo $(VERSION) > $(distdir)/.tarball-version

tests/database.scm

@@ -42,7 +42,8 @@
              (srfi srfi-64))
 
 (define (mailer)
-  (string-append "sendmail://" (getcwd) "/tests/mail.sh"))
+  (string-append "sendmail://"
+                 (search-path %load-path "tests/mail.sh")))
 
 ;; The above bash program will be invoked by mailutils.  It copies what's
 ;; passed on the standard input to the following file.