Added Makefile ergonomic features

These features are added in order to:

 1. Warn the user when root privileges are necessary
 2. Warn the user when root UID is probably not intended
 3. Bring the non-default 'example' target to the user's attention
    more clearly
 4. Build and install the util applications whenever the example app is
    built or installed, because the most likely use of the example app
    is to run the tests, which require the util applications
 5. Provide a new target 'util' for building the util applications
 6. Provide a new target 'install-example' for installing the example
    app
 7. Provide a new target 'mrproper' to uninstall and clean everything,
    in order to avoid missing files that need to be removed before
    regression testing, but might be forgotten, for example, the yang
    specs

Makefile.in

@@ -58,12 +58,28 @@ SUBDIRS1 = include lib
 SUBDIRS2 = apps etc yang # without include lib for circular dependency
 SUBDIRS= $(SUBDIRS1) $(SUBDIRS2)
 
-.PHONY:	doc example all clean depend $(SUBDIRS) install loc TAGS .config.status docker test
+.PHONY:	doc example install-example clean-example all clean depend $(SUBDIRS) \
+	install loc TAGS .config.status docker test util checkroot mrproper \
+	checkinstall warnroot
 
-all:	$(SUBDIRS2)
+all:	$(SUBDIRS2) warnroot
+	@echo "\e[32mAfter 'make install' as euid root, build example app and test utils: 'make example'\e[0m"
+
+checkroot:
+	@if [ "$${DESTDIR}" = "" -a $$(id -u) != "0" ]; \
+	then echo "\e[31mThis target must be made as euid root\e[0m"; exit 1; fi;
+
+warnroot:
+	@if [ $$(id -u) = 0 ]; \
+		then echo "\e[36mWarning: You built this target as uid root\e[0m"; exit 0; fi;
+
+checkinstall:
+	@if [ ! -f $(prefix)/include/clixon/clixon.h ]; then \
+	  echo "\e[31mclixon must be installed first to build this target. "\
+	  "Run 'make'. Then run 'make install' as root.\e[0m"; exit 1; fi; }
 
 # May cause circular include->include,lib
-$(SUBDIRS2): include lib # Cannot build app before lib (for parallel make -j)
+$(SUBDIRS2): $(SUBDIRS1) # Cannot build app before lib (for parallel make -j)
 	(cd $@ && $(MAKE) $(MFLAGS) all)
 
 $(SUBDIRS1): 
@@ -73,7 +89,8 @@ depend:
 	for i in $(SUBDIRS) doc example docker; \
 	do (cd $$i && $(MAKE) $(MFLAGS) depend); done
 
-install:  
+# Needs root permissions on most systems by default
+install: checkroot
 	for i in $(SUBDIRS) doc; \
 	do (cd $$i; $(MAKE) $(MFLAGS) $@)||exit 1; done; 
 	$(MAKE) $(MFLAGS) install-include
@@ -81,15 +98,30 @@ install:
 install-include:
 	for i in $(SUBDIRS) doc; \
 	do (cd $$i && $(MAKE) $(MFLAGS) $@)||exit 1; done; 
-	echo "To install example app: cd example; make; make install"
+	@echo "\e[32mTo install example app and test utils: make install-example\e[0m"
 
-uninstall:
+uninstall: checkroot
-	for i in $(SUBDIRS) doc example docker; \
+	for i in $(SUBDIRS) doc example util docker; \
 	do (cd $$i && $(MAKE) $(MFLAGS) $@)||exit 1; done; 
 
-doc:	
+doc: warnroot
 	cd $@; $(MAKE) $(MFLAGS) $@
 
+util:
+	cd $@; $(MAKE) $(MFLAGS)
+
+clean-example:
+	for i in example util; \
+	  do (cd $$i && $(MAKE) $(MFLAGS) clean) || exit 1; done;
+
+install-example: checkroot
+	for i in example util; \
+	  do (cd $$i && $(MAKE) $(MFLAGS) install) || exit 1; done;
+
+uninstall-example: checkroot
+	for i in example util; \
+	  do (cd $$i && $(MAKE) $(MFLAGS) uninstall) || exit 1; done;
+
 config.status:	configure
 	$(SHELL) config.status --recheck
 
@@ -97,14 +129,16 @@ configure:	configure.ac
 	cd $(srcdir) && autoconf
 
 clean:
-	for i in $(SUBDIRS) doc example docker; \
+	for i in $(SUBDIRS) doc example util docker; \
 		do (cd $$i && $(MAKE) $(MFLAGS) $@); done; 
 
+mrproper: uninstall uninstall-example clean clean-example
+
 distclean:
 	rm -f Makefile TAGS config.status config.log *~ .depend
 	rm -rf autom4te.cache build-root/rpmbuild
 	rm -f build-root/*.tar.xz build-root/*.rpm extras/rpm/Makefile
-	for i in $(SUBDIRS) doc example docker; \
+	for i in $(SUBDIRS) doc example util docker; \
 		do (cd $$i && $(MAKE) $(MFLAGS) $@); done
 
 export BR=$(CURDIR)/build-root
@@ -146,8 +180,10 @@ pkg-rpm: dist
 pkg-srpm: dist
 	make -C extras/rpm srpm
 
-example:	
+# To make the example you need to run the "install-include" target first
+example: checkinstall util warnroot
 	(cd $@ && $(MAKE) $(MFLAGS) all)
+	@echo "\e[36mRemember to run 'make install-example' as euid root\e[0m"
 
 # Run a clixon test container.
 # Alt: cd test; ./all.sh