lilypond-book needs a --safe mode

[John Williams]

lilypond-book does not work in --safe mode.

i.e.  lilypond-book --process='lilypond --safe -b eps' ...

Running lilypond...GNU LilyPond 2.9.28
Processing `/tmp/dp_latex/snippet-map.ly'
Parsing...ERROR: Unbound variable: ly:add-file-name-alist
command failed: lilypond --safe -b eps -I  "/tmp/dp_latex" --formats=eps 
-dread-file-list -deps-box-padding=-3  snippet-names
Child returned 1

Apparently this is because lilypond-book writes the snippet names out to a
"snippet-map.ly" file which is nothing more than a ly:add-file-name-alist
command, which is not allowed in --safe mode.  

The add-file-name-alist command only has a single line in the documentation, so
I cannot really figure out what it is doing.  Is it really necessary?  If I make
snippet-names contain the snippet-names, instead of "snippet-map.ly", it seems
compile the snippets ok.

(Well, mostly ok.  It outputs the music, but fails to include
"lilypond-book-preamble.ly", which seems to make the eps bounding boxes not get
set.)

~ John Williams