Log message:
net/libfilezilla: Set GCC_REQD=7 for C++17

Also, use the new c++17 keyword in USE_LANGUAGES.

This commit is not expected to change the produced binaries on any
system where it built before.

Log message:
*: recursive bump for nettle 3.5.1

Log message:
libfilezilla: update to 0.17.1.

0.17.1 (2019-06-21)

+ Added support for detached signatures
- Fixed crash if using the system trust store

0.17.0 (2019-06-17)

+ libfilezilla now requires C++17
+ Changed a lot of functions to use std::string_view
+ Added fz::socket_layer as base class for layers on top of sockets
+ Added fz::tls_layer, a Transport Layer Security layer, requiring GnuTLS 3.5.7 \ 
or later
+ Added fz::translate for gettext-style translatable strings. GNU Gettext is now \ 
a built-time (but not runtime) dependency
+ Added fz::bitscan and fz::bitscan_reverse to get the index of least and most \ 
significant bit set
+ Added fz::logger_interface as a base for logging system
- *nix: Small speed-up of fz::local_filesys through the use of fstatat()

Log message:
libfilezilla: update to 0.16.0.

2019-04-21 - libfilezilla 0.16.0 released
New features:

    Add fz::socket
    Add operator*= to fz::duration
    fz::event_loop can now also be created using fz::thread_pool or threadless.

Bugfixes and minor changes:

    fz::async_task now releases the thread back to the pool immediately when the \ 
task has completed without waiting for the join
    *nix: Fix file descriptor leaks on exec()

Log message:
Need pthread support, make sure a substitue is present if OS lacks support
natively, e.g Minix at present.

Log message:
libfilezilla: update to 0.15.1.

0.15.1 (2018-11-22)

+ Add argument to fz::strtok to return empty tokens
- Fix compatibility issue with Nettle < 3.3
- Fix fz::random_bytes on MinGW
- Fix memory leak in fz::buffer

0.15.0 (2018-10-19)

+ libfilezilla now depends on Nettle >= 3.1
+ Added fz::sha512, fz::sha256, fz::sha1 and fz::md5 hash functions
+ Added fz::hash_accumulator
+ Added fz::hmac_sha256 HMAC function
+ Added asymmetric encryption scheme using X25519
+ Added signature scheme using Ed25519
- Changed and documented semantics of the return value of fz::remove_file, \ 
removing a non-existing file is not an error

0.14.0 (2018-10-04)

+ Added fz::equal_insensitive_ascii
+ Added insensitive_ascii parameter to fz::starts_with and fz::ends_with
- Fixed namespace of to_wstring in wx glue

0.13.2 (2018-09-21)

- Fix regression in fz::shared_value::clear
- Fix parsing of URIs without path

0.13.1 (2018-09-10)

+ Made fz::scoped_lock movable
- Fix a few compiler warnings

Log message:
libfilezilla: update to 0.13.0.

0.13.0 (2018-07-16)

+ Add bool return value to replace_substrings to indicate whether something has \ 
been replaced.
+ fz::sprintf: Added %c format specifier
- MSW: Work around problematic DLL export of templates, timers now work if \ 
libfilezilla has been built as DLL

Log message:
libfilezilla: update to 0.12.3.

0.12.3 (2018-06-08)

+ Event handlers can now removed themselves while inside a callback
+ Added fz::query_string::pairs()

Log message:
libfilezilla: update to 0.12.2.

0.12.2 (2018-05-05)

+ Added parameters to base64_encode to control alphabet and padding
+ Improved performance of less_insensitive_ascii
+ *nix: Faster conversion between UTF-8 and wchar_t strings.

Log message:
libfilezilla: update to 0.12.1.

0.12.1 (2018-02-23)

+ Added fz::buffer::operator== and operator!=
- Fixed bug in fz::buffer::get(size_t)

0.12.0 (2018-02-16)

+ Added fz::datetime::operator bool
+ Added fz::datetime::get_rfc822 and fz::datetime::set_rfc822