Directs lilypond option help to stderr (issue 5625052)

[PhilEHolmes]

Reviewers: dak, Graham Percival,

Message:
Please review minor change.

Description:
The regtest option-help.ly prints out the help string for ly:set-option,
with the intention of making this testable via logfile comparison.
However, it sends the output to stdout, so it appears on the terminal
screen during make doc, and is never visible in the logfile and so is
not actually tested.  Patch sends the output to stderr - which is
unbuffered and therefore no flush is required.

Please review this at http://codereview.appspot.com/5625052/

Affected files:
  M lily/program-option-scheme.cc


Index: lily/program-option-scheme.cc
diff --git a/lily/program-option-scheme.cc b/lily/program-option-scheme.cc
index  
cf5416ae8b3325ea89fce6c890e5e7a7b7e2ebea..130fe469325a22f2c1a42f707727aa932d8e219a  
100644
--- a/lily/program-option-scheme.cc
+++ b/lily/program-option-scheme.cc
@@ -191,8 +191,7 @@ LY_DEFINE (ly_option_usage, "ly:option-usage", 0, 0, 0,  
(),
            "Print @code{ly:set-option} usage.")
 {
   string help = get_help_string ();
-  puts (help.c_str ());
-  fflush (stdout);
+  fputs (help.c_str (), stderr);

   return SCM_UNSPECIFIED;
 }