Issue 3925: lilypond -d leads to weird output

Issue 3925: lilypond -d leads to weird output

C++ string manipulation is a fragile bolt-on onto the type system.

"-" + 'd'

evaluates to a pointer 100 bytes after a constant string "-" in the data
section.  This fixes this bug, and also changes the fixed message from

    lilypond: option `-d, `--define-default'' requires an argument

to

    lilypond: option `-d, --define-default' requires an argument

In general, it does not appear to make sense quoting the long options
while not quoting the short options.