#5495 Add warning message for unknown code in fret-diagram-verbose

[Carl Sorensen]

Add warning message for unknown code in fret-diagram-verbose

This patch does not change the printed or midi output; it only
generates a warning on the console and in the logfile. Because
there is no change to the printed output, I felt like there was
no need for a regression test.

You can see the effect of this patch by running the following code:

\version "2.19.82"

{
s1^\markup{
\fret-diagram-verbose #'(
(please harakiri 1 5)
)
}
}

which will create a blank fret diagram and print a warning message in the
log.

http://codereview.appspot.com/570540043

[Anonymous]

Passes make, make check and a full make doc.

[Anonymous]

Patch on countdown for March 18th

[Carl Sorensen]

New patch uploaded responding to Harm's comments; git-cl updated the status but didn't record the message.

[Anonymous]

Passes make, make check and a full make doc.

[Anonymous]

Patch on countdown for March 24th

[Anonymous]

Patch counted down - please push to staging.

[Anonymous]

Patch counted down - please push to staging.

[Carl Sorensen]

Pushed to staging as 1b1b06d..45dedd4