Move cd-s to allow relative path parameters

All paths are now treated as relative to the working directory ($HERE)
when the script is called.
Download a debian package list and simplify it

This script downloads a gzip-ed debian package list; default is from TC5:
http://distro.ibiblio.org/tinycorelinux/5.x/x86/debian_wheezy_main_i386_Packages.gz

The list is downloaded and gunzip-ed, then stripped of everything except
package names and download paths. The resulting output file looks something
like this:

    libaac-tactics-ocaml pool/main/a/aac-tactics/libaac-tactics-ocaml_0.2.pl2-7_i386.deb
    libaac-tactics-ocaml-dev pool/main/a/aac-tactics/libaac-tactics-ocaml-dev_0.2.pl2-7_i386.deb
    python-aafigure pool/main/a/aafigure/python-aafigure_0.5-3_all.deb
    libaa-bin pool/main/a/aalib/libaa-bin_1.4p5-40_i386.deb
    libaa1 pool/main/a/aalib/libaa1_1.4p5-40_i386.deb

Each package name is followed by a space, then a relative path for a debian
mirror server. The resulting file can be quickly searched by grep.
Add bin/download-deb-pkg script

Downloads .deb package files from a debian mirror of your choice given the
package name and the file list downloaded by download-deb-pkg-list.

The parameters are listed in the file, but there is no help text for manual
usage (since this is supposed to be invoked by build-bundle-file.sh)
Use bin/deb2tcz.sh and company to install .debs

Debian packages can be added to the same mirror-extensions.lst and
builtin-extensions.lst, and are identified by a .deb extension. They are then
downloaded by bin/download-deb-pkg and converted by bin/deb2tcz.sh. In the case
of builtin extensions, the name is appended to onboot.lst.