Prepare for dependency vendoring.

- Add helper script to simplify glide usage.
- Add validation script for unwanted changes to vendoring.
- Relax/tighten up .{git,docker}ignore to cover vendored files properly.
- .validate: Protect from unbound variable in case of nounset setting.
- Install more recent hg version in the build container.
- Remove glide installation steps from Dockerfile.
- Update documentation.

script/glide.sh

@@ -0,0 +1,119 @@
+#!/bin/bash
+set -o errexit
+set -o pipefail
+set -o nounset
+
+####
+### Helper script for glide[-vc] to handle specifics for the Traefik repo.
+##
+# In particular, the 'integration/' directory contains its own set of
+# glide-managed dependencies which must not have its nested vendor folder
+# stripped. Depending on where the script is called from, it will do the Right
+# Thing.
+#
+
+CWD="$(pwd)"; readonly CWD
+GLIDE_ARGS=()
+GLIDE_VC_ARGS=(
+  '--use-lock-file'       # `glide list` seems to miss test dependencies, e.g., github.com/mattn/go-shellwords
+  '--only-code'
+  '--no-tests'
+)
+
+usage() {
+  echo "usage: $(basename "$0") install | update | get <package> | trim
+install: Install all dependencies and trim the vendor folder afterwards (alternative command: i).
+update:  Update all dependencies and trim the vendor folder afterwards (alternative command: up).
+get:     Add a dependency and trim the vendor folder afterwards.
+trim:    Trim the vendor folder only, do not install or update dependencies.
+
+The current working directory must contain a glide.yaml file." >&2
+}
+
+is_integration_dir() {
+  [[ "$(basename ${CWD})" = 'integration' ]]
+}
+
+if ! is_integration_dir; then
+  GLIDE_ARGS+=('--strip-vendor' '--skip-test')
+fi
+
+if ! type glide > /dev/null 2>&1; then
+  echo "glide not found in PATH." >&2
+  exit 1
+fi
+
+if ! type glide-vc > /dev/null 2>&1; then
+  echo "glide-vc not found in PATH." >&2
+  exit 1
+fi
+
+if [[ ! -e "${CWD}/glide.yaml" ]]; then
+  echo "no glide.yaml file found in the current working directory" >&2
+  exit 1
+fi
+
+if [[ $# -lt 1 ]]; then
+  echo "missing command" >&2
+  usage
+  exit 1
+fi
+
+readonly glide_command="$1"
+shift
+
+skip_glide_command=
+case "${glide_command}" in
+  'install' | 'i')
+    if [[ $# -ne 0 ]]; then
+      echo "surplus parameters given" >&2
+      usage
+      exit 1
+    fi
+    ;;
+
+  'update' | 'up')
+    if [[ $# -ne 0 ]]; then
+      echo "surplus parameters given" >&2
+      usage
+      exit 1
+    fi
+    ;;
+
+  'get')
+    if [[ $# -ne 1 ]]; then
+      echo 'insufficient/surplus arguments given for "get" command' >&2
+      usage
+      exit 1
+    fi
+    GLIDE_ARGS=("$1" "${GLIDE_ARGS[@]}")
+    shift
+    ;;
+
+  'trim')
+    if [[ $# -ne 0 ]]; then
+      echo "surplus parameters given" >&2
+      usage
+      exit 1
+    fi
+    skip_glide_command=yes
+    ;;
+
+  *)
+    echo "unknown command: ${glide_command}" >&2
+    usage
+    exit 1
+esac
+readonly skip_glide_command
+
+if [[ -z "${skip_glide_command}" ]]; then
+  # Use parameter substitution to account for an empty glide arguments array
+  # that would otherwise lead to an "unbound variable" error due to the nounset
+  # option.
+  GLIDE_ARGS=("${GLIDE_ARGS+"${GLIDE_ARGS[@]}"}")
+  echo "running: glide ${glide_command} ${GLIDE_ARGS[*]}"
+  glide ${glide_command} ${GLIDE_ARGS[*]}
+fi
+
+echo "trimming vendor folder using: glide-vc ${GLIDE_VC_ARGS[*]}"
+glide-vc ${GLIDE_VC_ARGS[*]}