release: check for pandoc

Abort releaseing if pandoc is missing.
(pandoc was not included in my essential app database, and thus missing on my new machine.)

devscripts/release.sh

@@ -33,6 +33,7 @@ if [ ! -z "`git status --porcelain | grep -v CHANGELOG`" ]; then echo 'ERROR: th
 useless_files=$(find youtube_dl -type f -not -name '*.py')
 if [ ! -z "$useless_files" ]; then echo "ERROR: Non-.py files in youtube_dl: $useless_files"; exit 1; fi
 if [ ! -f "updates_key.pem" ]; then echo 'ERROR: updates_key.pem missing'; exit 1; fi
+if ! type pandoc 2>/dev/null; then echo 'ERROR: pandoc is missing'; exit 1; fi
 
 /bin/echo -e "\n### First of all, testing..."
 make clean