Maintaing stats output format

Changed the first comment line to maintain output similar to that
produced by samtools stats.  Fixes bug where the sanity check in
parse_bamcheck1 would fail to detect the merged stats output as
a valid file.

Closes samtools#924

Author: betteridiot

misc/plot-bamstats

@@ -1184,7 +1184,7 @@ sub merge_bamcheck
         open($fh,'>',"$$opts{prefix}merge.bchk") or error("$$opts{prefix}merge.bchk: $!\n");
     }
 
-    print $fh "# This file was produced by plot-bamstats, the command line was:\n#   $$opts{args}\n#\n";
+    print $fh "# This file was produced by plot-bamstats and can be plotted using plot-bamstats\n# The command line was $$opts{args}\n";
 
     for my $sec (@{$$opts{sections}})
     {
@@ -1401,6 +1401,3 @@ sub create_html
 
     close($fh);
 }
-
-
-