This adds the shell function `wrapFactor`. This function is intended to wrap
the result of calling `build.sh` in the shell environment so it can be executed
outside of the nix shell.
Example:
```
$ nix-shell
[nix-shell] $ ./build.sh bootstrap
...build factor vm and image...
[nix-shell] $ wrapFactor .
exit
$ ./factor
```
`wrapFactor` takes the path to the factor root dir as argument, and expects the
binary `factor` and the image file `factor.image` there and uses Nixpkgs'
`makeWrapper` to wrap the `factor` executable in-place with the correct
`LD_LIBRARY_PATH`. Afterwards, the factor executable can be called outside of
the nix-shell environment.
`buildFHSUserEnv` uses `chroot` to create a kind of sandbox environment. This
change uses a simpler mechanism, and also provides the necessary libraries for
running all the demos.
timor
Kye W. Shi