Configure sphinx to require 1.5 for building htmlhelp

* This version contains the fix for sphinx-doc/sphinx#2550 so we want to
  assume it is present and tidy up all the external links. However if
  needed (and you don't care about the external links being broken) you
  can locally remove this version requirement.

docs/Makefile

@@ -93,7 +93,7 @@ json:
 
 .PHONY: htmlhelp
 htmlhelp:
-	$(SPHINXBUILD) -b htmlhelp $(ALLSPHINXOPTS) $(BUILDDIR)/htmlhelp
+	$(SPHINXBUILD) -b htmlhelp -t htmlhelp $(ALLSPHINXOPTS) $(BUILDDIR)/htmlhelp
 	# Copy handwritten index file to output, overwriting auto-generated one
 	@cp renderdoc.hhk $(BUILDDIR)/htmlhelp
 	# Copy introduction page over index.html

docs/conf.py

@@ -294,3 +294,10 @@ html_context = {
     'show_source': False,
     'html_show_sourcelink': False,
 }
+
+# We need 1.5 and above for the htmlhelp links to be handled properly without
+# needing separate ugly _blank links. If you don't care about that, you can
+# disable this
+if(tags.has('htmlhelp')):
+	print("**** We require sphinx 1.5 for htmlhelp build to have the fix for issue #2550 ****")
+	needs_sphinx = '1.5'

docs/make.bat

@@ -120,7 +120,7 @@ if "%1" == "json" (
 )
 
 if "%1" == "htmlhelp" (
-	%SPHINXBUILD% -b htmlhelp %ALLSPHINXOPTS% %BUILDDIR%/htmlhelp
+	%SPHINXBUILD% -b htmlhelp -t htmlhelp %ALLSPHINXOPTS% %BUILDDIR%/htmlhelp
 	if errorlevel 1 exit /b 1
 	REM Copy handwritten index file to output, overwriting auto-generated one
 	copy renderdoc.hhk %BUILDDIR%\htmlhelp\

docs/make.sh

@@ -102,7 +102,7 @@ if [ $1 == "json" ]; then
 fi
 
 if [ $1 == "htmlhelp" ]; then
-	$SPHINXBUILD -b htmlhelp $ALLSPHINXOPTS $BUILDDIR/htmlhelp
+	$SPHINXBUILD -b htmlhelp -t htmlhelp $ALLSPHINXOPTS $BUILDDIR/htmlhelp
 	if [ $? != 0 ]; then exit 1; fi
 	# Copy handwritten index file to output, overwriting auto-generated one
 	cp renderdoc.hhk $BUILDDIR/htmlhelp