This is for ChangeLog/1.4304/ but with my patch applied to get
lilypond-book actually to generate LaTeX
lilypond-book should not generate \RequirePackage{graphics} but
\usepackage{graphics}. The former version is for use in Class files,
where '@' has the status of a letter. \usepackage{graphics} is
equivalent to:
\makeatletter\RequirePackage{graphics}\makeatother
and so loads the package in the right environment if used in the
preamble of a document file. It seems that:
\includegraphics{filename}
still works, but some of the other facilities of the graphics package
may be broken. this too may break in future versions of the graphics
package.