Merge #13954: Warn (don't fail!) on spelling errors. Fix typos reported by codespell.

f8a81f73ac lint: Add spell check linter (codespell) (practicalswift)
ada356208e Fix typos reported by codespell (practicalswift)

Pull request description:

  * Check for common misspellings using `codespell`.
  * Fix recently introduced typos reported by `codespell`.

Tree-SHA512: 9974c0e640b411c7d0ebc5b45de253c19bac7fe3002cd98601ff8da8db584224c2fd7d331aee3df612c9f2cfef540d647a9b4c5a1a73fd208dc93ce4bf9e5e3e

test/lint/lint-spelling.ignore-words.txt

@@ -0,0 +1,6 @@
+cas
+hights
+mor
+objext
+unselect
+useable

test/lint/lint-spelling.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env 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.
+#
+# Warn in case of spelling errors.
+# Note: Will exit successfully regardless of spelling errors.
+
+export LC_ALL=C
+
+IGNORE_WORDS_FILE=test/lint/lint-spelling.ignore-words.txt
+if ! codespell --check-filenames --disable-colors --quiet-level=7 --ignore-words=${IGNORE_WORDS_FILE} $(git ls-files -- ":(exclude)build-aux/m4/" ":(exclude)contrib/seeds/*.txt" ":(exclude)depends/" ":(exclude)doc/release-notes/" ":(exclude)src/leveldb/" ":(exclude)src/qt/locale/" ":(exclude)src/secp256k1/" ":(exclude)src/univalue/"); then
+    echo "^ Warning: codespell identified likely spelling errors. Any false positives? Add them to the list of ignored words in ${IGNORE_WORDS_FILE}"
+fi