* parse.c (write_exp_string): Complete rewrite to store string

	* parse.c (write_exp_string):  Complete rewrite to store string
	contants as a leading explicit length, followed by the string data,
	followed by a trailing explicit length.
	* eval.c (evaluate_subexp), expprint.c (print_subexp),
	parse.c (length_of_subexp), parse.c (prefixify_subexp):
	Use recorded explicit length of strings in expression elements,
	rather than strlen.  Adjust code to skip over strings stored in
	expression elements, and code to access strings, to account for
	new leading explicit size expression element.
	* parse.c (length_of_subexp):  Test for minimum endpos of 1, not
	0, to avoid negative expression element indices.
	* valops.c (search_struct_method):  Minor whitespace change.