The main effect here is to separate unit tests, library source and
executable source.

re #17

re #17

This makes their function a bit clearer.

#17

The changelog should reflect previous versions that have been in the
Debian archive - this collects those not previously merged, and adds one
for 6.0-1.

Homebrew's glibmm uses deprecated bits of glib:

  CXX      Render.o
In file included from Render.cc:16:
In file included from ./Render.h:23:
In file included from /usr/local/Cellar/pangomm/2.42.0_1/include/pangomm-1.4/pangomm/layout.h:31:
/usr/local/Cellar/glibmm/2.60.0_1/include/glibmm-2.4/glibmm/object.h:73:3: error: 'GParameter' is deprecated [-Werror,-Wdeprecated-declarations]
  GParameter* parameters;
  ^
/usr/local/Cellar/glib/2.62.0/include/glib-2.0/gobject/gparam.h:194:39: note: 'GParameter' has been explicitly marked deprecated here
typedef struct _GParameter      GParameter GLIB_DEPRECATED_TYPE_IN_2_54;
                                           ^
/usr/local/Cellar/glib/2.62.0/include/glib-2.0/glib/gversionmacros.h:770:49: note: expanded from macro 'GLIB_DEPRECATED_TYPE_IN_2_54'
# define GLIB_DEPRECATED_TYPE_IN_2_54           GLIB_DEPRECATED_TYPE
                                                ^
/usr/local/Cellar/glib/2.62.0/include/glib-2.0/glib/gmacros.h:1013:30: note: expanded from macro 'GLIB_DEPRECATED_TYPE'
#define GLIB_DEPRECATED_TYPE G_DEPRECATED
                             ^
/usr/local/Cellar/glib/2.62.0/include/glib-2.0/glib/gmacros.h:942:37: note: expanded from macro 'G_DEPRECATED'
#define G_DEPRECATED __attribute__((__deprecated__))
                                    ^

check-source will now verify code formatting using clang-format 6.0
(or later).

fixes #60

It is supplanted by backup policies.

re #59

UNTESTED

re #59

closes #57

re #57

re #57

https://github.com/Homebrew/homebrew-core/issues/37873

This is part of a planned future change to use clang-format to get
and check consistent formatting. Mostly it's blocked on tool version
issues but this bit can be brought forward.

...& add a checklist for all things not investigated.

fixes #56

re #49

Now that there can be more than one backup per day, we need to be more
careful about how we pick the oldest backup in a bucket.

See http://www.greenend.org.uk/rjk/rsbackup/decay.pdf for the argument
that it's the oldest backup in each bucket that is preserved.

re #49

Essentially this meant that second and subsequent backups on the same
day would be missed out from any internal processing (including
determining what to prune). They were still added to the database
(hence the tests passing) so the broken version should not have left
and inconsistent state and pruning should sort itself out in due course.

fixes #49

Something in the toolchain generates *.o.tmp not (directly) *.o.

fixes #51

re #18

fixes #34