pkgs: add expat1 2.1.0-1, needed by gettext-tools

We didn't need this before because previously we did
not actually build gettext-tools during bootstrap.
But the new dpkg depends on gettext-tools, so now we
do need it.
pkgs: add xz 5.0.5-2, needed by new dpkg

We need this as dpkg links against liblzma and the .deb format itself
will move to this compression format in the future.
pkgs: make xz essential
pkgs: add time-date-pm 1.16-1, needed by new dpkg
pkgs: make time-date-pm essential
pkgs: add objtools 2.22-3, needed by new dpkg

This is used for the new "automatic dependencies" code
pkgs: make objtools essential
pkgs: fix objtools to work in both 10.7 and 10.4 dists.
pkgs: update dpkg to 1.16.10 (with patches)
pkgs: add texinfo 5.1-2
perlmods: update the auto install list to avoid interaction during bootstrapping
perlmods: generate symbols file based on shlibs, for automatic dependencies

dpkg-shlibdep uses the symbols file to generate auto shlibs aka auto
depends. I worked very hard on this part and it took lots of work to get
this working, but it does. Basically one can put ${Shlibs} in the deb
file and once the work is completed dpkg-shlibdep would replace that
line in the control file with the actual deps based on the symbols used
and the symbols in the symbols files.

For a few examples, see:

https://wiki.debian.org/UsingSymbolsFiles
http://www.debian.org/doc/manuals/maint-guide/advanced.en.html

See also the last paragraph of this section of the Debian Policy Manual:

http://www.debian.org/doc/debian-policy/ch-sharedlibs.html#s-sharedlibs-depends
perlmods: fix .la files during build time, to allow md5sums support

The md5sums feature of dpkg records a MD5 checksum of each file
contained in a deb and installed on your system. This can be used
to perform an automatic integrity check of your system, checking
if the files on your file system have the correct checksum.
If not, then something or somebody must have modified the file
since it was installed (e.g. an intruder on your system).

For this it is important that files are not modified after installation.
But we did exactly that with .la files: We fixed them up in a
postinst script. Since this would break the md5sums mechanism,
we now perform this fixup already while building the .deb file.
perlmods: add Triggers info field

We create the triggers files in DEBIAN inside the final .deb from them.
A usage example of the new Triggers field looks like this:
```
Triggers: <<
  Activate: <<
    %p/foo
  <<
  Interest-noawait: <<
    %p/blah
  <<
<<
```
Currently, the following subfields are valid:
  activate, activate-noawait, interest, interest-noawait
perlmods: add new Debconf field
pkgs: make texinfo essential, change it to use triggers and more
pkgs+perlmods: remove apt from bootstrap

It is neither essential nor required and the new apt's deplist
is much too heavy for bootstrap.
perlmods: remove check for apt from scanpackages()

This check is superfluous, as all apt specific subroutines
already check for apt presence
perlmods: add validator warning for deprecated fields, deprecate InfoDocs
Add libncursesw5 to bootstrap to enable dselect build so we don't have a different copy of dpkg in bootstrap as we do in dists.  Doing this required adding libncusrsesw5 and it's shlibs to Bootstrap.pm so that it wouldn't stop to ask to install them via deps since neither is essential.