New version of install_packages

[Henning Glawe]

Moin,
I worked a bit on install_packages, the results are available on
http://www.physik.fu-berlin.de/~glaweh/fai/

Changes:
 * uses libapt-pkg-perl
 * as often as possible uses system(@list), thus avoids quoting
   shell metacharacters in package lists
 * works with regular expressions in package lists (in apt's
   understanding, everything containing '.', '*' or '?' is
   assumed to be a regex)
 * checks versioned pagackes (mutt>=1.5) before handing
   them to apt-get
 * filters out virtual packages (sarge's apt quits
   when encountering a virtual package and lists the
   real packages providing this virtual package)

Background:

When doing a soft transtion from "woody" to "sarge", this means keeping
both releases installable from the same FAI configuration, APT's support
for regular expressions comes in handy for replaced packages like

apt-get install .?(gmc|nautilus)

(the .? is only in there to make apt-get recognize this as a regular
expression)

For this to work with FAI's install_packages, quite a lot of changes are
necessairy because of two reasons:

    * apt-cache (used to filter out unavailable packages/typos) behaves
      differently than apt-get (no regexps, no versioned packages,
      doesn't throw an error on virtual packages)
    * the shell interprets many regex characters as metacharacters

At my department, we tested this already on both woody and sarge
installs, but I need some other people to test this, so Thomas can merge 
it into FAI.

-- 
c u
henning