Added per-task curdir. and chdir, pager_read/write, mmap and munmap calls.

They look like what they should look like, but untested.

tasks/fs0/include/task.h

@@ -18,6 +18,8 @@ struct tcb {
 	struct list_head list;
 	int fd[TASK_OFILES_MAX];
 	struct id_pool *fdpool;
+	struct vnode *curdir;
+	struct vnode *rootdir;
 };
 
 struct tcb *find_task(int tid);