Merge branch 'fix_sync' into 'master'

src/platform/linux/mod.rs

src/platform/pal/mod.rs

src/platform/redox/mod.rs

src/sync/cond.rs

src/sync/mod.rs

src/sync/pthread_mutex.rs

src/sync/rwlock.rs

tests/Makefile

tests/pthread/timeout.c

tests/test_helpers.h