Most of the infrastructure here is general, only the validation/dispatch
is hardcoded to a particular prefix.
A notable change in behaviour is that notmuch-config now opens the
database e.g. on every call to list, which fails with an error message
if the database doesn't exit yet.
The files (test) scripts source (with builtin command `.`) provides
information which the scripts depend, and without the `source` to
succeed allowing script to continue may lead to dangerous situations
(e.g. rm -rf "${undefined_variable}"/*).
At the end of all source (.) lines construct ' || exit 1' was added;
In our case the script script will exit if it cannot find (or read) the
file to be sourced. Additionally script would also exits if the last
command of the sourced file exited nonzero.
Previously we set up a way for the top level notmuch command to choose
which gpg binary was invoked by libgmime. In this commit we add the
(mostly boilerplate) code to allow the notmuch-config command to read
and write this path, and use it in the appropriate struct.
Update tests for new default variable
All test scripts to be executed are now named as T\d\d\d-name.sh,
numers in increments of 10.
This eases adding new tests and developers to see which are test scripts
that are executed by test suite and in which order.
