Merge branch 'js/async-thread'

* js/async-thread: fast-import: die_nicely() back to vsnprintf (reverts part of ebaa79f) Enable threaded async procedures whenever pthreads is available Dying in an async procedure should only exit the thread, not the process. Reimplement async procedures using pthreads Windows: more pthreads functions Fix signature of fcntl() compatibility dummy Make report() from usage.c public as vreportf() and use it. Modernize t5530-upload-pack-error. Conflicts: http-backend.c