Apport 2.7

Improvements:
 * packaging.py, get_file_package(): Add optional "release" and "arch"
   arguments for getting a file's package for a foreign release or
   architecture. Implement this for apt/dpkg backend.
 * packaging.py, install_packages(): Add optional "architecture" argument for
   creating a sandbox for a foreign architecture. Implement this for apt/dpkg
   backend.
 * When a report's architecture does not match the system architecture, try to
   use gdb-multiarch (if available, as packaged on Debian/Ubuntu), and set
   architecture and gnutarget accordingly in gdb. This supports x86, x86_64,
   and ARM for now, so that reports from all these architectures can be
   retraced on an x86_84 machine. (LP: #1044437)
 * launchpad.py: Add "architecture" option to process reports for a foreign
   architecture.
 * Add exceptions from package hooks to new HookError_<filename> report field,
   to make them more visible. Until now they were only written to stderr.
   (LP: #1086309)

Bug fixes:
 * Fix test_find_package_desktopfile test to not consider packages with only
   one "NoDisplay=true" .desktop file for the "has one desktop file" test.
 * report.py, mark_ignore(): Use home directory of actual effective user, not
   of $HOME. Fixes ignore file when using through sudo.
 * apport-cli: Fix showing of prompt. Thanks Dmitry Shachnev!
 * fileutils.py, mark_report_upload(): Do not try to remove the .uploaded file,
   as this is not owned by the user.
 * backends/packaging-apt-dpkg.py, install_packages(): Set mirror to the one in
   the sandbox config.
 * apportcheckresume: Fix crash if state file does not exist.