python26: unbreak build (revert from db5 to db44)

The bsddb module is apparently not compatible with db5 (or db48), so switch
back to db44. Fixes the following build error:

  $ nix-build -A python26.modules
  these derivations will be built:
    /nix/store/5zcqmpa4iby0aa342psjph0byiyikm6h-python-bsddb-2.6.8.drv
  building path(s) `/nix/store/qpsjyx7nmxhm9zq40674wr67dx8w6ycl-python-bsddb-2.6.8'
  building /nix/store/qpsjyx7nmxhm9zq40674wr67dx8w6ycl-python-bsddb-2.6.8
  unpacking sources
  unpacking source archive /nix/store/2qwc1kd8allnaljm1z360lv9jsf8cfqy-Python-2.6.8.tar.bz2
  source root is Python-2.6.8
  patching sources
  applying patch /nix/store/cfk04ans56xql9l6waqhqzzd60g9rzxi-search-path.patch
  patching file setup.py
  Hunk #1 succeeded at 424 (offset 145 lines).
  applying patch /nix/store/dxscwf37hgq0xafs54h0c8xx47vg6d5g-nix-store-mtime.patch
  patching file Python/import.c
  Hunk #1 succeeded at 747 (offset -4 lines).
  configuring
  building
  running build_ext
  INFO: Can't locate Tcl/Tk libs and/or headers
  Traceback (most recent call last):
    File "./setup.py", line 2037, in <module>
      main()
    File "./setup.py", line 2032, in main
      'Lib/smtpd.py']
    File "/nix/store/xxzwak31qql6vq7v35xmq68zmjpfr5py-python-2.6.8/lib/python2.6/distutils/core.py", line 152, in setup
      dist.run_commands()
    File "/nix/store/xxzwak31qql6vq7v35xmq68zmjpfr5py-python-2.6.8/lib/python2.6/distutils/dist.py", line 975, in run_commands
      self.run_command(cmd)
    File "/nix/store/xxzwak31qql6vq7v35xmq68zmjpfr5py-python-2.6.8/lib/python2.6/distutils/dist.py", line 995, in run_command
      cmd_obj.run()
    File "/nix/store/xxzwak31qql6vq7v35xmq68zmjpfr5py-python-2.6.8/lib/python2.6/distutils/command/build_ext.py", line 340, in run
      self.build_extensions()
    File "./setup.py", line 249, in build_extensions
      longest = max([len(e.name) for e in self.extensions])
  ValueError: max() arg is an empty sequence
  builder for `/nix/store/5zcqmpa4iby0aa342psjph0byiyikm6h-python-bsddb-2.6.8.drv' failed with exit code 1
  error: build of `/nix/store/5zcqmpa4iby0aa342psjph0byiyikm6h-python-bsddb-2.6.8.drv' failed