Fix install target in man/Makefile.am

Commit 39c6dab89bbea9fe336f869b65e33102ba238205 introduced a regression:
make install during a package build in a tree generated by make dist would
no longer install the manual page... because they are already built and
available in $(srcdir) while $(CURDIR) was ok for the case where the
manual pages are not pre-built.

No we try both paths and pick the first one that exists.

debian/changelog

@@ -1,8 +1,13 @@
 dpkg (1.15.8.4) UNRELEASED; urgency=low
 
+  [ Guillem Jover ]
   * Fix use after free segfault on update-alternatives --remove-all.
     Closes: #591653, #591654
 
+  [ Raphaël Hertzog ]
+  * Fix make -C man install so that it actually finds the manual pages
+    to install. Closes: #591588
+
  -- Guillem Jover <guillem@debian.org>  Thu, 05 Aug 2010 17:42:51 +0200
 
 dpkg (1.15.8.3) unstable; urgency=low

man/Makefile.am

@@ -50,6 +50,8 @@ install-data-local-yes:
 		for trans in $(dist_man_MANS); do \
 			if [ -f $(CURDIR)/$$lang/$$trans ]; then \
 				files="$$files $(CURDIR)/$$lang/$$trans"; \
+			elif [ -f $(srcdir)/$$lang/$$trans ]; then \
+				files="$$files $(srcdir)/$$lang/$$trans"; \
 			fi; \
 		done; \
 		$(MAKE) install-man \