plasma_attr.h - add __attribute_always_inline__
Makefile - add dependency on plasma/*.h headers
implement plasma_atomic_lock_* as inline functions

implement plasma_atomic_lock_* as inline functions
add support macros plasma_atomic_xchg_*
add support macros plasma_atomic_st_*_release_*
plasma_spin_lock_* basic spinlock implementation

plasma_spin_lock_* basic spinlock implementation
plasma_spin_lock_init()
plasma_spin_lock_acquire()
plasma_spin_lock_acquire_try()
plasma_spin_lock_acquire_spinloop()
plasma_spin_lock_acquire_spindecay()
plasma_spin_lock_release()
plasma_spin_yield()
Makefile - add plasma_atomic.o and plasma_spin.o
nss_mcdb.c - do not hold lock while accessing mmap

nss_mcdb.c - do not hold lock while accessing mmap
(access to file-backed mmap might block while servicing page fault)
use plasma_spin_lock* to protect ref-counted mcdb