Add igor target to run igor(1) on the manuals.

doc/Makefile.in

@@ -26,6 +26,7 @@ top_srcdir = @top_srcdir@
 
 # Tools to use
 SED = @SED@
+IGOR = igor
 MANDOC = @MANDOCPROG@
 MANCOMPRESS = @MANCOMPRESS@
 MANCOMPRESSEXT = @MANCOMPRESSEXT@
@@ -97,6 +98,19 @@ PACKAGE_TARNAME = @PACKAGE_TARNAME@
 
 all: $(DEVDOCS) $(DOCS)
 
+igor: all
+	@if [ "$(mantype)" != "mdoc" ]; then \
+	    echo "make igor only supported for mdoc manuals" 1>&2; \
+	    exit 1; \
+	else \
+	    rval=0; \
+	    for m in $(DOCS); do \
+		echo $(IGOR) -D $$m; \
+		$(IGOR) -D $$m || rval=`expr $$rval + $$?`; \
+	    done; \
+	    exit $$rval; \
+	fi
+
 lint: all
 	@if [ "$(mantype)" != "mdoc" ]; then \
 	    echo "make lint only supported for mdoc manuals" 1>&2; \