IRB: rescue LoadError on require 'irb/*'

Catches bad ruby installations.

#1262

calabash-cucumber/scripts/.irbrc

@@ -1,6 +1,17 @@
-require "irb/completion"
-require "irb/ext/save-history"
-require "benchmark"
+begin
+  require "irb/completion"
+  require "irb/ext/save-history"
+rescue LoadError => e
+  puts %Q[
+Caught a LoadError while requiring an irb module.
+
+#{e}
+
+An error like this usually means your ruby installation is corrupt.
+
+]
+  exit(1)
+end
 
 begin
   require "awesome_print"
@@ -25,6 +36,8 @@ $ gem install calabash-cucumber
   exit(1)
 end
 
+require "benchmark"
+
 AwesomePrint.irb!
 
 ARGV.concat ["--readline", "--prompt-mode", "simple"]