Minor build system updates for doxygen.

The configure script has been updated to check for the doxygen and dot
applications (from doxygen and graphviz).  The results from these checks
are now used in the Makefile to ensure that the tools are installed when
you run "make doxygen".  If they are not, it will generate a helpful
error message.

Signed-off-by: Russell Bryant <russell@russellbryant.net>
Reviewed-by: Steven Dake <sdake@redhat.com>

Makefile.am

@@ -94,8 +94,19 @@ endif
 lint:
 	for dir in lcr lib exec services tools test; do make -C $$dir lint; done
 
+.PHONY: doxygen
 doxygen:
-	mkdir -p doc/api && doxygen
+	@if [ "$(DOXYGEN)" = "" ] || [ "$(DOT)" = "" ] ; then \
+		echo "*********************************************" ; \
+		echo "***                                       ***" ; \
+		echo "*** You must install doxygen and graphviz ***" ; \
+		echo "*** to generate the API documentation.    ***" ; \
+		echo "***                                       ***" ; \
+		echo "*********************************************" ; \
+		exit 1 ; \
+	else \
+		mkdir -p doc/api && $(DOXYGEN) ; \
+	fi
 
 dist-clean-local:
 	rm -f autoconf automake autoheader test_lense.sh

configure.ac

@@ -63,6 +63,8 @@ AC_PROG_RANLIB
 AC_CHECK_PROGS([GROFF], [groff])
 AC_CHECK_PROGS([PKGCONFIG], [pkg-config])
 AC_CHECK_PROGS([AUGTOOL], [augtool])
+AC_CHECK_PROGS([DOT], [dot])
+AC_CHECK_PROGS([DOXYGEN], [doxygen])
 
 # Checks for libraries.
 AC_CHECK_LIB([dl], [dlopen])