Stamp the build version into the binary (closes #253)

internal/versionscript/doc.go

@@ -0,0 +1,12 @@
+// Package versionscript holds the tests for script/version and for the
+// build files that consume it. It carries no runtime code: the version
+// string is produced by a shell script at build time and reaches the
+// binary through a linker flag, so nothing in the Go build graph can
+// assert it, but the behaviour still has to be verified by the test
+// suite.
+//
+// The files under test are outside the Go build graph, so `go test`'s
+// result cache serves a stale PASS when only script/version, the
+// Makefile or the Dockerfile changed: run the container build, or
+// GOFLAGS=-count=1, to trust a result here after editing them.
+package versionscript