Dont check source packages against installed obsoletes

- Regression originating from somewhere around commit
  781cfed0fd, obsoletes from installed
  packages were matched against the package being built.
  Building obsoleted packages needs to be possible, they could be for
  an older distro for example.

lib/depends.c

@@ -525,6 +525,10 @@ int rpmtsCheck(rpmts ts)
 	    checkInstDeps(ts, dcache, p, RPMTAG_CONFLICTNAME, rpmdsN(provides));
 	}
 
+	/* Skip obsoletion checks for source packages (ie build) */
+	if (rpmteIsSource(p))
+	    continue;
+
 	/* Check package name (not provides!) against installed obsoletes */
 	checkInstDeps(ts, dcache, p, RPMTAG_OBSOLETENAME, rpmteN(p));
     }