Peter Wu authored Nov 24, 2018 and Philip Withnall committed Nov 27, 2018

opendir and closedir are not async-signal-safe, these may call malloc
under the hood and cause a deadlock in a multi-threaded program.
This only affected Linux when /proc is mounted, other systems use a
slower path that iterates through all potential file descriptors.
Fixes a long-standing problem (since GLib 2.14.2).

Closes #945 and #1014