clarifications

[Christopher Fry <cfry@OZ.AI.MIT.EDU>]

130: Self-evaluating forms (such as strings] in tagbodies
     are no-ops but otherwise harmless.
     Its not worth it to make a special case to rule them out.
     Code (or humans) that write/modify other code shouldn't have to worry
     about what's in the body that its wrapping a tagbody around.

268: Can the proposed COPY be installed like SETF?
     Call it COPYF. Depth of copying could be specified with
     an integer.

425: Along with FILE-LENGTH, it would be nice to be
     able to ask the operating system how much 
     disk-space is available in a given directory,
     so you could have some control when attempting to
     write too-large files without going through
     some error mechanism.
     (disk-free-space pathname) => number of bytes available.