Datums with 7 parameter transformations does not work

[cjpersson]

All predefined datums that are defined with 7-parameter transforms gives completely wrong results when projecting. This applies to the datums IRE65, NZGD49 and OSGB36. This also means that all CRSs defined with with these datums fails conversions. This for instance includes the British National Grid systems.

The problem comes from that internally the last 4 parameters should be converted to different units than they are defined in (sek->rad, 1->1/1M). This is done if conversion parameters are defined with the +towgs84 parameter but not for predefined datums.

I have enclosed a patch that does conversions for datums.

[cjpersson]

Patch that fixes 7-parameter transforms for datums.