These are extension modules for PostgreQL 9.1
to allow postgis modules
to be installed using standard PostgreSQL 9.1+
CREATE EXTENSION syntax

To use: first make install regular PostGIS
then do the below for each extension

make 
make install 

each

Then in your PostgreSQL database run
CREATE EXTENSION postgis_core;
CREATE EXTENSION postgis_raster;
CREATE EXTENSION postgis_topology;

Known issue:
To uninstall postgis_core you have to drop cascade the extension
which is not ideal but working out the cast issues.

The dependency logic should warn if you try
to install postgis_raster without postgis_core, 
but that seems to not be working right
thought drop cascade extension postgis_core drops
postgis_raster extension.