Bug#750189: python-apt: compare_to_version_in_cache() not aware of multiarch

[Limbo Peng <iwinux@gmail.com>]

Package: python-apt
Version: 0.9.3.6
Severity: normal

Dear Maintainer,

python-apt fails to find installed packages of different architecture
when reading metadata from a deb file. For example, I've installed
libopenjpeg5:i386 on an amd64 system:


```
$ apt-cache policy libopenjpeg5:i386
libopenjpeg5:i386:
  Installed: 1.5.2-2
  Candidate: 1.5.2-2
  Version table:
 *** 1.5.2-2 0
        500 http://ftp.cn.debian.org/debian/ unstable/main i386 Packages
        100 /var/lib/dpkg/status

limbo@Skypiea in ~/.vim/bundle/YouCompleteMe [master]
$ apt-cache policy libopenjpeg5
libopenjpeg5:
  Installed: (none)
  Candidate: 1.5.2-2
  Version table:
     1.5.2-2 0
        500 http://ftp.cn.debian.org/debian/ unstable/main amd64 Packages
```

But when I use python-apt to read the deb file, it reports that this
package is NOT installed on my system:

```python
from apt.debfile import DebPackage
pkg = DebPackage('/var/cache/apt/archives/libopenjpeg5_1.5.2-2_i386.deb')
print pkg.compare_to_version_in_cache() == DebPackage.VERSION_SAME # => False
print pkg.compare_to_version_in_cache() == DebPackage.VERSION_NONE # => True
```

I think the problem resides in function `compare_to_version_in_cache()`
in `debfile.py`, which does not check package names appended with
architecture name suffix.

-- System Information:
Debian Release: jessie/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.12.14-debian (SMP w/4 CPU cores; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages python-apt depends on:
ii  libapt-inst1.5     1.0.3
ii  libapt-pkg4.12     1.0.3
ii  libc6              2.18-7
ii  libgcc1            1:4.9.0-5
ii  libstdc++6         4.9.0-5
ii  python             2.7.6-2
ii  python-apt-common  0.9.3.6

Versions of packages python-apt recommends:
ii  iso-codes    3.53-1
ii  lsb-release  4.1+Debian12
ii  xz-utils     5.1.1alpha+20120614-2

Versions of packages python-apt suggests:
pn  python-apt-dbg  <none>
pn  python-apt-doc  <none>
ii  python-gtk2     2.24.0-3+b1
ii  python-vte      1:0.28.2-5

-- no debconf information