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Currently we try to use the proj.4 strings to store references to coordinate
systems (eg. for the default project crs). Unfortunately the proj.4
string isn't unique in our database:

sqlite> select count(*),parameters from tbl_srs group by parameters order by count(*) desc limit 10;
54|+proj=longlat +ellps=intl +no_defs
27|+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs
21|+proj=longlat +ellps=clrk80 +no_defs
17|+proj=longlat +ellps=bessel +no_defs
15|+proj=longlat +ellps=clrk66 +no_defs
13|+proj=longlat +a=6378249.2 +b=6356515 +no_defs
11|+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs
9|+proj=longlat +ellps=GRS80 +no_defs
9|+proj=longlat +ellps=krass +no_defs
9|+proj=tmerc +lat_0=0 +lon_0=105 +k=1 +x_0=500000 +y_0=0 +ellps=krass +units=m +no_defs
sqlite> select auth_name,auth_id,description,parameters from tbl_srs where parameters='+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs' limit 1;
EPSG|4148|Hartebeesthoek94|+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

So selecting 'EPSG:4326' as default CRS results in 'EPSG:4148 - Hartebeesthoek94' - which obviously is irritating.

The attached patch switches to the use of authid instead of proj.4 strings. Any objections to commit it for 1.7?