simulation: Add a simulatied UART input device.  Also lots of misc clean-up for stylistic compatibility with other architectures

Repartition some message queue logic: sched/mqueue should have all mqueue knowledge; fs/mqueue should deal only with inodes

Fix some unbalanced sched_lock()/sched_unlock() pairs int the re-implemented VFS semaphore and message queue logic

Convert mqueue structure for use in VFS as inode data; rename mqueue_inode_s; remove links, reference counts and name from mqueue structure.  These will be replaced by VFS data.  Remove g_msgqueues and mq_findnamed.c; these will be replace with VFS logic

Fix some comments:  Remove button description from GPIO interrupt handlers that derive from the button interrupt handler

More vfork():  If we get to vfork() via system call, then we need to clone some system call information so that the return form the cloned system call works correctly

Fix vfork().  Now that arguments are kept on the stack, the way that arguments are passed from parent to child in vfork() must change.  This bug has always been present, but was not visible with the old strdup() way of passing arguments