Make install-tests target work with vpath builds

Also add a top-level install-tests target.

Backpatch to all live branches.

Craig Ringer, tweaked by me.

GNUmakefile.in

@@ -72,6 +72,7 @@ $(call recurse,check-world,src/test src/pl src/interfaces/ecpg contrib src/bin,c
 $(call recurse,checkprep,  src/test src/pl src/interfaces/ecpg contrib src/bin)
 
 $(call recurse,installcheck-world,src/test src/pl src/interfaces/ecpg contrib src/bin,installcheck)
+$(call recurse,install-tests,src/test/regress,install-tests)
 
 GNUmakefile: GNUmakefile.in $(top_builddir)/config.status
 	./config.status $@

src/test/regress/GNUmakefile

@@ -87,8 +87,8 @@ regress_data_files = \
 
 install-tests: all install install-lib installdirs-tests
 	$(MAKE) -C $(top_builddir)/contrib/spi install
-	for file in $(regress_data_files); do \
-	  $(INSTALL_DATA) $$file '$(DESTDIR)$(pkglibdir)/regress/'$$file || exit; \
+	for file in $(subst $(srcdir)/,,$(regress_data_files)); do \
+		$(INSTALL_DATA) $(srcdir)/$$file '$(DESTDIR)$(pkglibdir)/regress/'$$file || exit; \
 	done
 
 installdirs-tests: installdirs