[Therion] Debian therion using system libproj needs testing

[Wookey]

The latest therion debian package (5.3.16-3) uses the system libproj
library, not the embedded version included in the therion source (this
is good practice for various reasons and should have been done a while
ago).

Currently the system libproj is 4.8 whilst the therion-inlcuded
version is 4.7. These seems compatible for the (farily simple) usage
therion makes, but I'd like people who use this to check that it still
works the same as before.

(I've run it on the cheddar dataset and things still come in in the
right place so it appears to work OK :-)

Currently in the experimental suite:
https://packages.debian.org/source/experimental/therion

Wookey
-- 
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