Bug: irb_require incorrectly matches similarly named files

[GabrielLidenor]

IRB's irb_require command can incorrectly treat a file as already loaded when another file with a similar name has been loaded.

For example, after loading foo2.rb, running:

irb_require "foo"

Expected behavior

irb_require "foo" should load foo.rb even when foo2.rb has already been loaded.

Actual behavior

irb_require "foo" is treated as already loaded because foo2.rb is considered a match.

Reproduction

1. Create foo.rb and foo2.rb.
2. Run irb_require "foo2".
3. Run irb_require "foo".
4. Observe that foo.rb is not loaded.