kernel changes

[Matthias Radestock]

I've made the following changes to the kernel

1) Added a description of the symbol lookup mechanism. I also made a
   change in the VM that will result in not-resolved-at-compile-time
   symbols to be lookup up in both the local and global env, instead
   of just the local env.
2) fixed 'load-file mechanism to deal with read errors.
3) Made Reader 8-bit clean - it used to break when receiving input
   >x7F.
4) improved efficiency of mapNx and mapN by using pre-constructed
   result tuples instead of iteratively built ones.
5) The security mechanism for TCP/IP connections now defaults to "no
   security", thus making it backwards compatible with currently
   deployed systems.
6) The "telnet access" feature is now using the new TCP/IP code, thus
   enabling introduction of access authorization mechanism.


The code has been checked in but not installed.


Matthias