minor: tool to check if extension is installed

bin/fail_if_no_c.rb

@@ -0,0 +1,11 @@
+# Fail if the C extension module isn't installed.
+#
+# Only really intended to be used by internal build scripts.
+
+require 'rubygems'
+require 'mongo'
+begin
+  require 'mongo_ext/cbson'
+rescue LoadError
+  Process.exit 1
+end