* cppfiles.c: Include splay-tree.h, not hashtab.h.
	(redundant_include_p, make_IHASH, hash_IHASH, eq_IHASH): Delete.
	(destroy_include_file_node): New.
	(_cpp_init_include_hash): Rename _cpp_init_include_table.
	Create a splay tree, not a hash table.
	(open_include_file): Look up the path in the include table,
	do the multiple include optimization here, etc.
	(cpp_included): Walk the path.
	(find_include_file): Just walk the path calling
	open_include_file, or call it directly for an absolute path.
	(_cpp_fake_ihash): Rename _cpp_fake_include and update for new
	scheme.
	(read_include_file): Update for new scheme.  Don't close the
	file unless reading fails.
	(_cpp_execute_include, cpp_read_file): Tweak for new scheme.

	* cpphash.h (struct ihash, NEVER_REINCLUDE): Delete.
	(struct include_file): New.
	(NEVER_REREAD, DO_NOT_REREAD, CPP_IN_SYSTEM_HEADER): New
	macros.
	(CPP_PEDANTIC, CPP_WTRADITIONAL): Update.
	Update prototypes.

	* cppinit.c: Include splay-tree.h.
	(cpp_reader_init, cpp_cleanup): Update.

	* cpplib.h (struct cpp_buffer): Change ihash field to
	'struct include_file *inc'.  Remove system_header_p.
	(struct cpp_reader): Change all_include_files to a
	struct splay_tree_s *.

	* cpplex.c: Update all references to cpp_buffer->ihash and/or
	cpp_buffer->system_header_p.
	(cpp_pop_buffer): Close file here, only if DO_NOT_REREAD.

From-SVN: r34636