Fixes to Enviornment variable handling (linking and purity)

 * Removed the LD_PRELOAD non-sense a better approach will soon be comming
 * Added lib64 to the list of library paths to add in LD_LIBRARY_PATH
 * Added an "overwrite" option for environment variable setting that
   replaces instead of appends to environment variables.
Fix error message that appears when an enviornment does not exists

Now that you explicitly create environments the error message should be
more clear.
Add the environment name to our basic PS1 change

This is still a stop gap measure but now that we have the information we
should add it in.
Basic ld.so indirection for Linux

In this setup we make sure there is always a lib/ld-linux-xpkg.so in our
environment, and that binaries built have their interp pointed their.
This is currently done with a build flag but if needed we can patch the
binaries.

This indirection link points to local ld.so in the environment if their is
one otherwise it points to the system ld.so. This allows for ld changes and
custom ld's without any other changes to the packages.