build: detect doc generation failure

Commit 8665f855 introduced a slight regression in doc generation,
since make only quits a rule on the first failed command ending
with a newline rather than a semicolon.

* docs/Makefile.am (html/index.html): Don't use xmllint unless
xsltproc succeeded.
* .gitignore: Ignore recently updated stamp file name.

.gitignore

@@ -50,6 +50,7 @@
 /mkinstalldirs
 /po/*
 /proxy/
+/python/generator.py.stamp
 /src/libvirt_iohelper
 /src/remote/*_client_bodies.h
 /src/remote/*_protocol.[ch]

docs/Makefile.am

@@ -155,7 +155,7 @@ internals/%.html.tmp: internals/%.html.in subsite.xsl page.xsl sitemap.html.in
 html/index.html: libvirt-api.xml newapi.xsl page.xsl sitemap.html.in
 	$(AM_V_GEN)if [ -x $(XSLTPROC) ] ; then \
 	  $(XSLTPROC) --nonet -o $(srcdir)/ \
-	  $(srcdir)/newapi.xsl $(srcdir)/libvirt-api.xml ; fi ; \
+	  $(srcdir)/newapi.xsl $(srcdir)/libvirt-api.xml ; fi && \
 	if test -x $(XMLLINT) && test -x $(XMLCATALOG) ; then \
 	  if $(XMLCATALOG) '$(XML_CATALOG_FILE)' "-//W3C//DTD XHTML 1.0 Strict//EN" \
 	    > /dev/null ; then \