also add dev repos when using a beta

prepare-opam.sh

@@ -26,7 +26,7 @@ if [[ -z "$FRESH_OPAM" ]]; then # skip if this is a fresh opam root
 fi
 
 # Make sure we got the right set of repositories registered
-if echo "$@" | fgrep "dev" > /dev/null; then
+if echo "$@" | egrep "(dev|beta)" > /dev/null; then
     # We are compiling against a dev version of something.  Get ourselves the dev repositories.
     test -d "$OPAMROOT/repo/coq-extra-dev" || opam repo add coq-extra-dev https://coq.inria.fr/opam/extra-dev -p 0
     test -d "$OPAMROOT/repo/coq-core-dev" || opam repo add coq-core-dev https://coq.inria.fr/opam/core-dev -p 5