bt full - to include args and locals.

set print sevenbit on
  - it is more useful to be able to see the exact bytes
    (in case something is dumped as a string and not hexadecimal digits)
set print static-members off
  - there are many interesting (non-const) static members
set frame-arguments all
  - even non-printables are useful to see.

Let's make our bb logs give a little bit more detail on those
hard to reproduce bugs.

Tests on rhel7's gdb-7.6.1-120.el7

mtr detects a forced combination if the command line for a test already
includes all options from this combination. options are stored in a perl
hash as (key,value) pairs.

this breaks if the command line has two options with the same name,
like --plugin-load-add=foo --plugin-load-add=bar, and the combination
forces plugin foo.

In particular, this resulted in warnings when running
federated.federatedx_versioning test