util.c: add support for additional escape characters in string_quote

util.c: add support for additional escape characters in string_quote

Quotes are not always used to denote string limits; printfd uses angle
brackets for that, for example.  As result, mechanism for supplying
set of additional characters in order to avoid ambiguities regarding
the end of the quoted string is needed.

* defs.h (string_quote): Add escape_chars parameter.
(print_quoted_string_ex): New function prototype.
* util.c (string_quote): Add escape_chars parameter.
(print_quoted_string_ex): Rename from print_quoted_string, add
escape_chars parameter, pass it to string_quote call.
(print_quoted_string): Turn into a thin wrapper around
print_quoted_string_ex.
(printstr_ex): Pass NULL as escape_chars argument of string_quote call.
* socketutils.c (unix_parse_response): Pass NULL as escape_chars
argument of string_quote call.
* tests/print_quoted_string.c (print_octal): New function.
print_quoted_memory_ex): Use it.  Add escape_chars parameter.
(print_quoted_memory): Pass NULL as escape_chars argument
of print_quoted_memory_ex call.
* tests/tests.h (print_quoted_string_ex, print_quoted_memory_ex): Add
escape_chars parameter.
* tests/fsync-y.c: Pass NULL as escape_chars argument of
print_quoted_string_ex call.

Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>