Modified so the header files in the subdirectories can be found in the compilations...

Modified so the header files in the subdirectories can be found in the compilations performed by 'make DISTCHECK_CONFIGURE_FLAGS=--disable-japanese distcheck'.

That is done by:
	1) Adding nostdinc to AUTOMAKE_OPTIONS
	2) Defining DEFAULT_INCLUDES to have -I$(srcdir) and -I$(top_builddir)/src (those are what it would have had without nostdinc in AUTOMAKE_OPTIONS)
	3) Adding a -I$(srcdir)/<subdir> (i.e. -I$(srcdir)/world) for each of the subdirectories where there's header files that have to be found