Various fixes, streamlining, and better conformance to Debian conventions

* Removed URL_FW_CONFIG definition, as it is not used (but see note below on /etc/fw_env.config)

* Replaced dummy/transitional packages in EXTRA_PACKAGES with their successors: module-init-tools -> kmod, uboot-envtools & uboot-mkimage -> u-boot-tools

* Added "dialog" to EXTRA_PACKAGES to allow debconf dialogs to work

* Removed KERNEL_VERSION definition, as it's no longer needed (and is prone to falling out of date anyway)

* Fixed RO_ROOT_ typo (thanks to the anonymous forum poster who caught it)

* Hide error message from RO_ROOT test, for polish

* Fixed "is_readonly=0" typo (also thanks to anonymous forum poster)

* Fixed typos in Perl check: missing apostrophe, and "[" has "=" as an operator, not "=="

* Removed superfluous semicolons from shell conditionals

* Need to do "-d $ROOT", not "-f $ROOT" as $ROOT is a directory

* Removed SRC definition, as it is not used

* tar(1) function letters should not be prefixed with a hyphen

* Add security.debian.org line to /etc/apt/sources.list, to keep the system abreast of security updates

* Instead of creating /etc/apt/apt.conf, drop a fragment into /etc/apt/apt.conf.d/ (more appropriate for such small config additions)

* The mkimage invocations are not needed; the flash-kernel package already generates uImage/uInitrd correctly during debootstrap

* Added the nice comment header (with minor edits) from $URL_FW_CONFIG to /etc/fw_env.config, and spaced out the hex values to line up with the column-header comment

* Append to /etc/network/interfaces instead of overwriting it, to keep the original file comment header and a layout more like regular Debian systems have

* Tweaked the alignment of columns in /etc/fstab

* Removed the /tmp tmpfs entry from /etc/fstab, in favor of setting RAMTMP=1 in /etc/default/tmpfs

* Don't create (overwrite) /etc/kernel/postinst.d/zz-flash-kernel, since the flash-kernel package already provides [a better version of] this script

* Added some comments to explain what's going on with /etc/inittab et al.

* HWCLOCKACCESS=no belongs in /etc/default/hwclock as of Wheezy

* CONCURRENCY=shell is obsolete according to /etc/init.d/rc, and some mailing-list messages indicate that this setting can sometimes cause the boot-up process to fail, so this is probably best done away with

* Don't clobber /etc/shadow with a single line; just edit the entry for root and leave the others untouched

* Run "apt-get clean" after we're done to clear out 50+ MB of .deb files
Ported over applicable changes from kirkwood.debian-wheezy.sh

Additionally:

* Install linux-image-kirkwood metapackage instead of linux-image-2.6-kirkwood, as 2.6 gets installed anyway on Squeeze

* Fixed here-document quoting on zz-flash-kernel

* Renamed zz-flash-kernel script to zz-doozan-flash-kernel, not to conflict [nor be confused with] with a potential zz-flash-kernel script installed by the flash-kernel package
Ported over applicable changes from kirkwood.debian-wheezy.sh

Additionally:

* Install linux-image-kirkwood instead of linux-image-2.6-kirkwood, as 2.6 gets installed anyway on Squeeze

* Install "dialog" package to avoid configuration errors during debootstrap

* Don't kill hbwd process until after the user gives the go-ahead

* debootstrap needs --no-gpg-check or else it complains about a bad signature

* Don't remove original vmlinuz and initrd.img files, as System.map and config files still remain, and the user might need to regenerate uImage/uInitrd anyway

* Fixed backslash escaping in double-quoted sed pattern

* Added standard /etc/fstab comment header

* Simplified sed pattern containing slashes to avoid "leaning toothpicks"

* Do "rm -f ..." instead of "rm ... >/dev/null 2>&1"
Ported over applicable changes from kirkwood.debian-wheezy.sh

Additionally:

* "[" has "=" as an operator, not "=="
Fixed HTML errors and updated Debian packages link
Merge pull request #4 from iskunk/drg-mods

Fixes, updates, streamlining