* Travis fix to collect coredumps from build configuration subdirs - #720

Previously, Travis would only attempt to collect coredumps from the last
directory the build script was in, or the home directory. This meant
that most coredumps were missed, and debug information was lost.

The new setup configures apport to watch for crashes on any executables
(by default it watches for executables from Ubuntu packages). These
crash dumps are picked up, extracted, and analysed using GDB to provide
a backtrace (this needs the executable to be passed to GDB as well so
that debug symbols are provided).

* Restructured .travis.yml to avoid underspecified builds.