Let's be sure that this script is executed in a correct Docker image

Test: xdebug

install-php-extensions

@@ -12,6 +12,11 @@
 set -o errexit
 set -o nounset
 
+if ! which docker-php-ext-configure >/dev/null || ! which docker-php-ext-enable >/dev/null || ! which docker-php-ext-install >/dev/null || ! which docker-php-source >/dev/null; then
+	printf 'The script %s is meant to be used with official Docker PHP Images - https://hub.docker.com/_/php\n' "$0" >&2
+	exit 1
+fi
+
 # Reset the Internal Field Separator
 resetIFS() {
 	IFS='