NETTLE check failing on Debian

I've resolved a couple build errors already by [installing some undocumented prerequisites on the Debian-based image](https://github.com/Quantisan/privatise-data-release-service/blob/b02d0339dadb4b35709370f292354497b11b784b/Dockerfile#L8). But I'm still getting this error:

```
checking for NETTLE... configure: error:
***
*** Libnettle 2.7 was not found.

===============================[ ERROR: GnuTLS ]================================

failed process: Process(setenv(`/usr/local/.julia/v0.3/GnuTLS/deps/src/gnutls-3.2.14/configure --prefix=/usr/local/.julia/v0.3/GnuTLS/deps/usr`,Union(UTF8String,ASCIIString)["PATH=/usr/local/.julia/v0.3/GnuTLS/deps/usr/bin:/usr/local/julia/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin","NETTLE_LIBS=-L/usr/local/julia//lib -L/usr/local/.julia/v0.3/GnuTLS/deps/usr/lib -lnettle -lgmp","PWD=/","JULIA_PKGDIR=/usr/local/.julia/","JULIA_PATH=/usr/local/julia","LD_LIBRARY_PATH=/usr/local/julia//lib:/usr/local/.julia/v0.3/GnuTLS/deps/usr/lib","JULIA_VERSION=0.3.9","JULIA_VER=0.3","CPPFLAGS= -I/usr/local/.julia/v0.3/GnuTLS/deps/usr/include -I/usr/local/.julia/v0.3/GnuTLS/deps/usr/include -I/usr/local/julia//include","LDFLAGS= -L/usr/local/.julia/v0.3/GnuTLS/deps/usr/lib -L/usr/local/.julia/v0.3/GnuTLS/deps/usr/lib -L/usr/local/julia//lib -Wl,-rpath -Wl,/usr/local/.julia/v0.3/GnuTLS/deps/usr/lib","HOGWEED_LIBS=-L/usr/local/julia//lib -L/usr/local/.julia/v0.3/GnuTLS/deps/usr/lib -lhogweed -lgmp","PKG_CONFIG_PATH=/usr/local/.julia/v0.3/GnuTLS/deps/usr/lib/pkgconfig","LIBS=-lgmp ","HOME=/root","HOSTNAME=eadddbb61a32"]), ProcessExited(1)) [1]
while loading /usr/local/.julia/v0.3/GnuTLS/deps/build.jl, in expression starting on line 55

================================================================================
```

I'm working on getting it to work. Will post an update if I find a solution. In the mean time, any pointer would be appreciated!

Start with the linked Dockerfile and reproduce the Debian-based image build, then inspect /usr/local/.julia/v0.3/GnuTLS/deps/build.jl around line 55 and the failing GnuTLS configure command. Check how the NETTLE dependency is discovered in that environment; done means the GnuTLS dependency build completes without the Libnettle 2.7 error.

Written by the indexing model from the issue text.