Fixed a dependency in user_manual's makefile.

doc/user_manual/makefile

@@ -7,11 +7,14 @@ EXAMPLE_DIR = $(SRCDIR)/examples/three_parents_F2
 
 all: user_manual.pdf
 
+.FORCE:
+
 user_manual.pdf: spell-pedigree.tex detection.tex outputs.tex pipeline.tex pop.tex spell-marker.tex spell-qtl.tex spell-qtl-examples.tex version.tex user_manual.tex images/Spell-pipeline2.svg images/full_map.png images/logo_MIAT.png pdfs/by-sa.pdf pdfs/gpl-v3-logo.pdf .inputs .outputs 
 	pdflatex --shell-escape user_manual.tex && pdflatex --shell-escape user_manual.tex 
 
-version.tex: 
-	git tag | tail -1 > version.tex
+version.tex: .FORCE
+	git tag | tail -1 > /tmp/last-tag
+	diff /tmp/last-tag $@ || cat /tmp/last-tag > $@
 
 spell-pedigree.tex: $(SRCDIR)/doc/man/spell-pedigree.1.md
 	/usr/bin/pandoc $(SRCDIR)/doc/man/spell-pedigree.1.md --listings -f markdown -t latex -o spell-pedigree.tex