Input paths are now parsed at the beginning and components
put into an ordered linked list headed by struct pathdata.
Lookup functions use these components to look up vnodes.
Dirbuf allocation was broken, fixed it.
Added more comments on reading directories.
Issues: fs0 ought to check buf address for sys_readdir(). Currently
test0 is passing an area on its stack and fs0 is writing the data to its own
address space (i.e. an area on its own stack.)
We now have a single dirbuf of size PAGE_SIZE kept on the vnode. This is
to be used for directory contents only. The reason it's kept on FS0 is
because the contents are modified by calls such as mkdir or create, and otherwise
these would have been handled by mm0 on the page cache buffers, which wouldn't work.
Boot files and tasks are now initialised together. Theads can ask for particular
space and thread ids, if they're unused. This enables us to get predefined ids for
known tasks such as the VFS task.
Fixes to README
Other minor fixes.
