libfmt version 9 broke the API by removing fmt::make_args_checked().

Fixes https://bugs.debian.org/1014543

Fixes
../git/src/Log.hxx:121:42: error: no member named 'forward' in namespace 'std'
        LogFormat(LogLevel::ERROR, e, fmt, std::forward<Args>(args)...);
Signed-off-by: Khem Raj <raj.khem@gmail.com>

"DEFAULT" is a bad name - all it says is that it's the default value,
but it doesn't say what it means.  The name NOTICE mimics the syslog
level.

Make LogError()/FormatError() wrappers for those.  Now we can log
exceptions with a lower level.

Prepare for templated functions.

Make LogError()/FormatError() wrappers for those.  Now we can log
exceptions with a lower level.

Prepare for templated functions.

Map LogLevel::INFO to G_LOG_LEVEL_INFO, and LogLevel::DEFAULT to
G_LOG_LEVEL_MESSAGE.  Now client connect/disconnect message are only
logged on log_level "secure".

Copy the according file from another project (i.e. XCSoar).  This will
allow copying more code more easily.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Replaces GLib's GError.

Don't free the string right after calling log_init_file().  Add a new
function log_deinit() that frees the string on shutdown.

This fixes cycling the log file after SIGHUP (Mantis ticket 0003524).

Use GLib the logging functions g_debug(), g_error() instead.