Nfd update

[Azaezel]

No description provided.

[Areloch]

With the default settings, looks to work fine on Ubuntu, no issues noted.
Also looks to work fine in Win. Need to test on the mac before merge-in to be sure it's all kosher(And give a run of the zenity mode to ensure that plays nice as at least an alternate mode)

[jmdejong]

I think you need to add nfd_gtk.c to the blacklist when using zenity, otherwise it will just run gtk anyways.

There's a few bugs in nfd zenity:

Torque3D/Engine/lib/nativeFileDialogs/nfd_zenity.c

Line 95 in 8304168

char* prefix = "--filename";

This should be char* prefix = "--filename="; instead. See also mlabbe/nativefiledialog#60

Torque3D/Engine/lib/nativeFileDialogs/simple_exec.h

Line 124 in 8304168

release_assert(waitpid(pid, &status, 0) == pid);

waitpid will always error (return -1) when the handler for SIGCHLD is set to SIG_IGN (which is the default).
https://stackoverflow.com/questions/22681021/waitpid-with-execl-used-in-child-returns-1-with-echild/24599676#24599676
This can be fixed by setting an empty handler for SIGCHLD.
See mlabbe/nativefiledialog#61 for my proposed solution.
Alternatively the assertion could be removed.