Hack it a bit differently so that it works with texlive 2013, see http://bugs.gentoo.org/480862
Turns out this patch is required also for texlive 2012, see http://bugs.gentoo.org/517474

--- doc/Makefile.am
+++ doc/Makefile.am
@@ -29,7 +29,7 @@ if BUILD_DOCUMENTATION
 if USE_LATEX
 	rm -f latex/libcaca.tex latex/libcaca.pdf
 	mv latex/refman.tex latex/libcaca.tex
-	sed 's/setlength{/renewcommand{/' latex/libcaca.tex \
+	sed 's/\\setlength{/%\0/' latex/libcaca.tex \
 	  | sed 's/.*usepackage.*times.*//' > latex/refman.tex
 	cd latex && $(MAKE) $(AM_CFLAGS) refman.pdf || (cat refman.log; exit 1)
 	mv latex/refman.pdf latex/libcaca.pdf