Protection agains non-existing subdirectories for clean and clobber

targets.  On some platforms this would cause an infinite Make
recursion.  Also remove "Doc" from the SUBDIRSTOO variable, since it
no longer exists in the standard distribution.

Makefile.in

@@ -146,7 +146,7 @@ OPT=		@OPT@
 SUBDIRS=	Parser Objects Python Modules
 
 # Other subdirectories
-SUBDIRSTOO=	Include Lib Doc Misc Demo Grammar
+SUBDIRSTOO=	Include Lib Misc Demo Grammar
 
 # Files and directories to be distributed
 CONFIGFILES=	configure configure.in acconfig.h config.h.in Makefile.in
@@ -485,11 +485,13 @@ localclean:
 
 clean:		localclean
 		-for i in $(SUBDIRS); do \
+		    if test -d $$i; then \
 			(echo making clean in subdirectory $$i; cd $$i; \
 			 if test -f Makefile; \
 			 then $(MAKE) clean; \
 			 else $(MAKE) -f Makefile.*in clean; \
 			 fi); \
+		    else true; fi; \
 		done
 
 localclobber:	localclean
@@ -498,11 +500,13 @@ localclobber:	localclean
 
 clobber:	localclobber
 		-for i in $(SUBDIRS); do \
+		    if test -d $$i; then \
 			(echo clobbering subdirectory $$i; cd $$i; \
 			 if test -f Makefile; \
 			 then $(MAKE) clobber; \
-			 else $(MAKE) -f $(srcdir)/Makefile.in clobber; \
+			 else $(MAKE) -f $(srcdir)/Makefile*.in clobber; \
 			 fi); \
+		    else true; fi; \
 		done
 
 # Make things extra clean, before making a distribution: