Add curl utility

Crafty Docker doesn't have access to curl, wget, netcat, etc. This
helper script adds the ability to download a file.

server-properties/helpers/curl.sh

@@ -0,0 +1,19 @@
+function __curl() {
+  read -r proto server path <<<"$(printf '%s' "${1//// }")"
+  if [ "$proto" != "http:" ]; then
+    printf >&2 "sorry, %s supports only http\n" "${FUNCNAME[0]}"
+    return 1
+  fi
+  DOC=/${path// //}
+  HOST=${server//:*}
+  PORT=${server//*:}
+  [ "${HOST}" = "${PORT}" ] && PORT=80
+
+  exec 3<>"/dev/tcp/${HOST}/$PORT"
+  printf 'GET %s HTTP/1.0\r\nHost: %s\r\n\r\n' "${DOC}" "${HOST}" >&3
+  (while read -r line; do
+   [ "$line" = $'\r' ] && break
+  done && cat) <&3
+  exec 3>&-
+}
+