attempt at reproducible tarballs (sdist)

contrib/build-linux/sdist/Dockerfile

@@ -0,0 +1,16 @@
+FROM ubuntu:18.04@sha256:b58746c8a89938b8c9f5b77de3b8cf1fe78210c696ab03a1442e235eea65d84f
+
+ENV LC_ALL=C.UTF-8 LANG=C.UTF-8
+
+RUN apt-get update -q && \
+    apt-get install -qy \
+        git \
+        gettext \
+        python3 \
+        python3-pip \
+        python3-setuptools \
+        faketime \
+        && \
+    rm -rf /var/lib/apt/lists/* && \
+    apt-get autoremove -y && \
+    apt-get clean