[postgis-devel] liblwgeom versioning

[Sandro Santilli]

In order to fix the topology performance regression in PostGIS 2.2.0
I had to change the topology section of the liblwgeom ABI and API:

[1] https://trac.osgeo.org/postgis/ticket/3321

As we want to ship the fix in PostGIS 2.2.1 but still avoid to
trigger crashes from any binary dynamically-linking to liblwgeom
the library SONAME needed to be changed.

To make such management easier in the future, I moved liblwgeom
versions from configure.ac to Version.config, where  they are
manually set (rather than derived from PostGIS release number).

Liblwgeom versionins uses libtool's current/age/revision triplet,
currently set to 3:0:0.

The SONAME of liblwgeom will still include Major and Minor PostGIS
release version, so we'll be able to keep numebers low, enough that
for 2.3.0 we might start back from 1:0:0 (not done in 2.2.0 because
we started already with an interface higher than 1).

I'm not sure it's safe to use 3:0:0 given PostGIS-2.2.0 shipped
with a liblwgeom of 4:2:0 (decrementing current?).
The resulting SONAME on Linux is "liblwgeom-2.2.so.3" whereas it
was "liblwgeom-2.2.so.2" for PostGIS-2.2.0, but I don't know if
on other systems there could be a different outcome (Bas?).

I've added this info in the HOWTO_RELEASE file.

I believe this is a good compromise between liblwgeom independence
and easy of maintainance in PostGIS.

--strk;

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