Merge branch 'pid' into 'master'

fmt.sh

redox-rt/src/arch/aarch64.rs

redox-rt/src/arch/i686.rs

redox-rt/src/arch/x86_64.rs

redox-rt/src/lib.rs

redox-rt/src/proc.rs

redox-rt/src/signal.rs

redox-rt/src/sys.rs

redox-rt/src/thread.rs

src/header/signal/mod.rs

src/ld_so/tcb.rs

src/platform/linux/signal.rs

src/platform/pal/signal.rs

src/platform/redox/mod.rs

src/platform/redox/signal.rs

src/pthread/mod.rs

tests/sigchld.c