revert naming change for log files

Commit 61ace80 changed to only add the .log suffix if the name didn't
contain a dot. I'm not at all sure why that was done, and it seems
completely wrong, since the tar command only picks up .log files. SO
make sure there is a .log suffix on every log file written.

Per report from Tomas Vondra.

Author: adunstan

run_build.pl

@@ -904,8 +904,7 @@ sub cleanlogs
 sub writelog
 {
     my $stage = shift;
-    my $fname = $stage;
-    $fname = "$fname.log" unless $fname =~ /\./;
+    my $fname = "$stage.log";
     my $loglines = shift;
     my $handle;
     my $lrname = $st_prefix . $logdirname;