* cppexp.c (parse_charconst): Null does not end character
	constants.
	* cppinit.c (ISTABLE): Null character handled as whitespace.
	* cpplex.c (null_warning):  new function.
	(skip_string): Emit warning if nulls encountered.
	(_cpp_skip_hspace): Emit warning if nulls encountered.
	(_cpp_lex_token): Emit warning if nulls encountered.  Drop
	them.
	* cpp.texi: Update.

From-SVN: r33013