Version reporting & module ABI change.

Version reporting & module ABI change.

Debug version display reports library info.

Bumps lookup API magic constant, adds new field to module API.

When invoking { exim -d -bV } we can display more version information.
Show versions for many external libraries, including both compile-time
and run-time information if we can.

Optional for modules, may be NULL.  Implemented for MySQL, SQLite &
Whoson lookups.  For all lookups, if dynamically loaded, report the
Exim version number from the build.  (Packagers will bundle stuff, but
dynamic modules are no longer just available for packagers, so we need
to deal with less managed environments and people forgetting to install
new modules).

Suggest in EDITME that users of modules not using package management
consider embedding a version number in the path to the modules.

Should consider removing the TLS (OpenSSL/GnuTLS) reporting from the
default -bV display and moving it into the debug display.  Not done.

Created version.h, now support a version extension string for
distributors who patch heavily. Henceforth release engineer should
change the version in version.h not version.c.