Look for rst2html same way we look for rst2man and make it non-optional

configure.ac

@@ -60,14 +60,16 @@ if test "x$SPHINX" = "xno"; then
 fi
 
 AC_ARG_WITH([rst2html],
-               AS_HELP_STRING([--with-rst2html=PATH],
-                              [Location of rst2html (auto)]),
-               [RST2HTML="$withval"],
-               [AC_CHECK_PROGS(RST2HTML, [rst2html rst2html.py], "no")
-	        if test "x$RST2HTML" = "xno"; then
-		   AC_MSG_WARN([rst2html not found - not building changelog])
-		fi])
-AM_CONDITIONAL(HAVE_RST2HTML,[test "x$RST2HTML" != "xno"])
+  AS_HELP_STRING([--with-rst2html=PATH], [Location of rst2html (auto)]),
+  [RST2HTML="$withval"],
+  AC_CHECK_PROGS(RST2HTML,
+     [rst2html rst2html.py rst2html-3.6 rst2html-3],
+     "no"))
+
+if test "x$RST2HTML" = "xno"; then
+   AC_MSG_ERROR(
+     [rst2html not found - (Weird, we found rst2man?!)])
+fi
 
 AC_ARG_WITH([dot],
   AS_HELP_STRING([--with-dot=PATH],

doc/Makefile.am

@@ -5,14 +5,7 @@ RST2ANY_FLAGS = --halt=2
 EXTRA_DIST = changes.rst changes.html
 
 changes.html: changes.rst
-if HAVE_RST2HTML
 	${RST2HTML} ${RST2ANY_FLAGS} $? $@
-else
-	@echo "========================================"
-	@echo "You need rst2html installed to make dist"
-	@echo "========================================"
-	@false
-endif
 
 # build graphviz before sphinx, so sphinx docs can use svg output
 SUBDIRS = graphviz sphinx