update build system and README

We should have a release on opam ASAP so that we can point to it in the README. We could also have a "dev" version on opam for people that want to depend on that one, but not use our crazy opam.pins hack.

build/opam-pins.sh

@@ -4,18 +4,23 @@ set -e
 ## Usage:
 ##   ./opam-pins.sh < opam.pins
 
+if ! which curl >/dev/null; then
+    echo "opam-pins needs curl. Please install curl and try again."
+    exit 1
+fi
+
 # Process stdin
 while read PACKAGE URL HASH; do
     if echo "$URL" | egrep '^https://gitlab\.mpi-sws\.org' > /dev/null; then
         echo "[opam-pins] Recursing into $URL"
         # an MPI URL -- try doing recursive pin processing
-        curl -f "$URL/raw/$HASH" 2> /dev/null | "$0"
+        curl -f "$URL/raw/$HASH/opam.pins" 2>/dev/null | "$0"
     fi
     if opam pin list | fgrep "$PACKAGE.dev.$HASH " > /dev/null; then
         echo "[opam-pins] $PACKAGE already at commit $HASH"
     else
         echo "[opam-pins] Applying pin: $PACKAGE -> $URL#$HASH"
         opam pin add "$PACKAGE.dev.$HASH" "$URL#$HASH" -k git -y -n
+        echo
     fi
-    echo
 done