Cleaned up the use of thread types

The THREAD type was not used everywhere and pthread_t was used instead.
The thread creation function also returned the address of a stack allocated
value which isn't guaranteed to be usable.

server/core/spinlock.c

@@ -87,7 +87,7 @@ spinlock_acquire(SPINLOCK *lock)
         }
     }
     lock->acquired++;
-    lock->owner = THREAD_SHELF();
+    lock->owner = thread_self();
     atomic_add(&(lock->waiting), -1);
 #endif
 }
@@ -112,7 +112,7 @@ spinlock_acquire_nowait(SPINLOCK *lock)
 #endif
 #if SPINLOCK_PROFILE
     lock->acquired++;
-    lock->owner = THREAD_SHELF();
+    lock->owner = thread_self();
 #endif
     return TRUE;
 }