Moving everything in src/ up a level

[ghudson@MIT.EDU]

Some time soon, Tom and I would like to cut the src directory out of
the krb5 tree, moving everything there to the top level.  The primary
motivator is making it reasonable to use an autoconf-controlled
Makefile for the doc directory.

>From the perspective of the build system proper, this is a trivial
change, but everything which automates or documents building the krb5
tree, or applies packages to it, will need adjustment--in particular,
OS packages.  I believe the changes should be simple makework, but
please speak up if this would be burdensome enough that we should try
to find another way.