Add linter: Make sure all shell scripts opt out of locale dependence using "export LC_ALL=C"

test/lint/lint-shell-locale.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+#
+# Copyright (c) 2018 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#
+# Make sure all shell scripts:
+# a.) explicitly opt out of locale dependence using "export LC_ALL=C", or
+# b.) explicitly opt in to locale dependence using the annotation below.
+
+export LC_ALL=C
+
+EXIT_CODE=0
+for SHELL_SCRIPT in $(git ls-files -- "*.sh" | grep -vE "src/(secp256k1|univalue)/"); do
+    if grep -q "# This script is intentionally locale dependent by not setting \"export LC_ALL=C\"" "${SHELL_SCRIPT}"; then
+        continue
+    fi
+    FIRST_NON_COMMENT_LINE=$(grep -vE '^(#.*|)$' "${SHELL_SCRIPT}" | head -1)
+    if [[ ${FIRST_NON_COMMENT_LINE} != "export LC_ALL=C" ]]; then
+        echo "Missing \"export LC_ALL=C\" (to avoid locale dependence) as first non-comment non-empty line in ${SHELL_SCRIPT}"
+        EXIT_CODE=1
+    fi
+done
+exit ${EXIT_CODE}