sh/merge-with-custom-msg: add checks [ci skip]

* Use 'set -e' to bail on any errors.
* If the pull request number is not specified, bail out.
* Print a simple pre-merge checklist before prompting for merge.

sh/merge-with-custom-msg

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+set -e
+
 usage() {
     local error="$1"
 
@@ -41,12 +43,29 @@ fi
 REV=$1
 PR=$2
 
+if [[ -z "$PR" ]]; then
+    usage "PULL_REQUEST not specified"
+fi
+
 KERNEL_CHANGED=`git diff --name-status $REV -- pkg/arvo/sys`
 PILLS_CHANGED=`git diff --name-status $REV -- bin`
 
+echo "Pre-merge checklist:"
+echo
+echo "Arvo:"
+echo "* Is this contribution OTA-updateable on top of the latest release?"
+echo "* Does this contribution include updated pills, if applicable?"
+echo
+echo "General:"
+echo "* Does this contribution contain tests for sanity checks, regressions, etc.?"
+echo "* Are commit prefixes present and accurate?"
+echo "* Have all WIP/FIXME/DONTCOMMIT commits been squashed?"
+echo "* Do commits contain long-form descriptions, if applicable?"
+echo
+
 if [[ ! -z $KERNEL_CHANGED && -z $PILLS_CHANGED ]]
 then
-  echo "WARNING: kernel has changed, but pills have not"
+  echo "**WARNING**: kernel has changed, but pills have not"
   echo $KERNEL_CHANGED
   echo
 fi