Docs: Always rebuild all docs

Previously, only calling "make clean && make html" would display all
errors and warnings in the docs. This was too slow to do by default, and
hence many errors would go unnoticed.
Adding the -a flag to Sphinx forces it to look at all the files again,
but is considerably quicker than deleting the build directory. As such,
I think it's good default behaviour as it isn't too slow even on
non-SSD machines.

docs/Makefile

@@ -37,38 +37,38 @@ clean:
 	-rm -rf $(BUILDDIR)/*
 
 html:
-	$(SPHINXBUILD) -b html $(ALLSPHINXOPTS) $(BUILDDIR)/html
+	$(SPHINXBUILD) -a -b html $(ALLSPHINXOPTS) $(BUILDDIR)/html
 	@echo
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."
 
 dirhtml:
-	$(SPHINXBUILD) -b dirhtml $(ALLSPHINXOPTS) $(BUILDDIR)/dirhtml
+	$(SPHINXBUILD) -a -b dirhtml $(ALLSPHINXOPTS) $(BUILDDIR)/dirhtml
 	@echo
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/dirhtml."
 
 singlehtml:
-	$(SPHINXBUILD) -b singlehtml $(ALLSPHINXOPTS) $(BUILDDIR)/singlehtml
+	$(SPHINXBUILD) -a -b singlehtml $(ALLSPHINXOPTS) $(BUILDDIR)/singlehtml
 	@echo
 	@echo "Build finished. The HTML page is in $(BUILDDIR)/singlehtml."
 
 pickle:
-	$(SPHINXBUILD) -b pickle $(ALLSPHINXOPTS) $(BUILDDIR)/pickle
+	$(SPHINXBUILD) -a -b pickle $(ALLSPHINXOPTS) $(BUILDDIR)/pickle
 	@echo
 	@echo "Build finished; now you can process the pickle files."
 
 json:
-	$(SPHINXBUILD) -b json $(ALLSPHINXOPTS) $(BUILDDIR)/json
+	$(SPHINXBUILD) -a -b json $(ALLSPHINXOPTS) $(BUILDDIR)/json
 	@echo
 	@echo "Build finished; now you can process the JSON files."
 
 htmlhelp:
-	$(SPHINXBUILD) -b htmlhelp $(ALLSPHINXOPTS) $(BUILDDIR)/htmlhelp
+	$(SPHINXBUILD) -a -b htmlhelp $(ALLSPHINXOPTS) $(BUILDDIR)/htmlhelp
 	@echo
 	@echo "Build finished; now you can run HTML Help Workshop with the" \
 	      ".hhp project file in $(BUILDDIR)/htmlhelp."
 
 qthelp:
-	$(SPHINXBUILD) -b qthelp $(ALLSPHINXOPTS) $(BUILDDIR)/qthelp
+	$(SPHINXBUILD) -a -b qthelp $(ALLSPHINXOPTS) $(BUILDDIR)/qthelp
 	@echo
 	@echo "Build finished; now you can run "qcollectiongenerator" with the" \
 	      ".qhcp project file in $(BUILDDIR)/qthelp, like this:"
@@ -77,7 +77,7 @@ qthelp:
 	@echo "# assistant -collectionFile $(BUILDDIR)/qthelp/django-oscar.qhc"
 
 devhelp:
-	$(SPHINXBUILD) -b devhelp $(ALLSPHINXOPTS) $(BUILDDIR)/devhelp
+	$(SPHINXBUILD) -a -b devhelp $(ALLSPHINXOPTS) $(BUILDDIR)/devhelp
 	@echo
 	@echo "Build finished."
 	@echo "To view the help file:"
@@ -86,45 +86,45 @@ devhelp:
 	@echo "# devhelp"
 
 epub:
-	$(SPHINXBUILD) -b epub $(ALLSPHINXOPTS) $(BUILDDIR)/epub
+	$(SPHINXBUILD) -a -b epub $(ALLSPHINXOPTS) $(BUILDDIR)/epub
 	@echo
 	@echo "Build finished. The epub file is in $(BUILDDIR)/epub."
 
 latex:
-	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
+	$(SPHINXBUILD) -a -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
 	@echo
 	@echo "Build finished; the LaTeX files are in $(BUILDDIR)/latex."
 	@echo "Run \`make' in that directory to run these through (pdf)latex" \
 	      "(use \`make latexpdf' here to do that automatically)."
 
 latexpdf:
-	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
+	$(SPHINXBUILD) -a -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
 	@echo "Running LaTeX files through pdflatex..."
 	make -C $(BUILDDIR)/latex all-pdf
 	@echo "pdflatex finished; the PDF files are in $(BUILDDIR)/latex."
 
 text:
-	$(SPHINXBUILD) -b text $(ALLSPHINXOPTS) $(BUILDDIR)/text
+	$(SPHINXBUILD) -a -b text $(ALLSPHINXOPTS) $(BUILDDIR)/text
 	@echo
 	@echo "Build finished. The text files are in $(BUILDDIR)/text."
 
 man:
-	$(SPHINXBUILD) -b man $(ALLSPHINXOPTS) $(BUILDDIR)/man
+	$(SPHINXBUILD) -a -b man $(ALLSPHINXOPTS) $(BUILDDIR)/man
 	@echo
 	@echo "Build finished. The manual pages are in $(BUILDDIR)/man."
 
 changes:
-	$(SPHINXBUILD) -b changes $(ALLSPHINXOPTS) $(BUILDDIR)/changes
+	$(SPHINXBUILD) -a -b changes $(ALLSPHINXOPTS) $(BUILDDIR)/changes
 	@echo
 	@echo "The overview file is in $(BUILDDIR)/changes."
 
 linkcheck:
-	$(SPHINXBUILD) -b linkcheck $(ALLSPHINXOPTS) $(BUILDDIR)/linkcheck
+	$(SPHINXBUILD) -a -b linkcheck $(ALLSPHINXOPTS) $(BUILDDIR)/linkcheck
 	@echo
 	@echo "Link check complete; look for any errors in the above output " \
 	      "or in $(BUILDDIR)/linkcheck/output.txt."
 
 doctest:
-	$(SPHINXBUILD) -b doctest $(ALLSPHINXOPTS) $(BUILDDIR)/doctest
+	$(SPHINXBUILD) -a -b doctest $(ALLSPHINXOPTS) $(BUILDDIR)/doctest
 	@echo "Testing of doctests in the sources finished, look at the " \
 	      "results in $(BUILDDIR)/doctest/output.txt."