build: Allow running sign-release target from the dist dir.

--

This is a kludge to avoid a new configure run only to then cd down do
dist.  Just cd to dist and run make sign-release.

(cherry picked from commit 178e4eb655)

Makefile.am

@@ -202,7 +202,7 @@ release:
 
 sign-release:
 	 +(set -e; \
-	  cd dist; \
+	  test $$(pwd | sed 's,.*/,,') = dist || cd dist; \
 	  x=$$(grep '^RELEASE_ARCHIVE=' $$HOME/.gnupg-autogen.rc|cut -d= -f2);\
           if [ -z "$$x" ]; then \
              echo "error: RELEASE_ARCHIVE missing in ~/.gnupg-autogen.rc">&2; \