[misc] Make release notes script usable against HEAD

Author: teo

hacking/release_notes.sh

@@ -1,4 +1,4 @@
 #!/bin/bash
-previous_tag=$(git describe --tags --abbrev=0 v$1^)
-echo "Commits from $previous_tag to v$1:"
-git log $previous_tag..v$1 --oneline --format="%s" --reverse|sort -s -k1.1,1.4
+previous_tag=$(git describe --tags --abbrev=0 $1^)
+echo "Commits from $previous_tag to $1:"
+git log $previous_tag..$1 --oneline --format="%s" --reverse|sort -s -k1.1,1.4