The variable GIT_VERSION is always defined, either obtained from Git or
a file that is embedded in tarballs when they are built. Optionally,
that version is declared as VERSION in config.h so it will be used e.g. in
the daemons when they print the version number.
There is a check that should catch missing tags (i.e. if the version number
in AC_INIT() isn't a prefix of the version obtained via Git).
The automatically determined path for systemd units is an absolute system
path that doesn't respect $(prefix). That's a problem for make distcheck,
which is usually ran as regular user and it's not expected to have any
impact on the system (it does a local install in a subdir). To avoid
these issues we override the configure flags used by make distcheck and
set the path to one relative to the specified prefix.
While 0909bf6c explicitly includes the whole source tree (to cover README.md),
this has the unpleasant side effect of covering a workspace under "testing"
with all its sources, or any other potential subdirectory that exists.
This configure flag enables lcov  coverage generation and is intended
to be used with unit tests (--enable-unit-tests is implied).
A html coverage report can be generated by issuing the following command
in the toplevel build directory:
 - http://ltp.sourceforge.net/coverage/lcov.php
Based on a patch by Adrian-Ken Rueegsegger.