Update documentation for upcoming stable release Debian/jessie
Use jessie as new default release
Add support for jessie in dialog based user interface
package selection: replace dhcp3-client with isc-dhcp-client

The dhcp3-client package no longer exists in Debian/jessie.
Support MKFS_OPTS variable + use -F option in mkfs.ext* when running in force mode
Add sources.list support for squeeze-lts
docs: simplify table of supported releases, mention lenny issue

We don't usually test with cdebootstrap, so there's no point
in listing this any longer.

While at it switch to the new asciidoc table format.
Make disk identifier configurable via DISK_IDENTIFIER variable

When using fixed disk identifiers for Virtual Machine
builds (using FIXED_DISK_IDENTIFIERS='yes').

Thanks: Patrick Schleizer <adrelanos@riseup.net> for the initial patch
Fixes: #28