Extend functionality of list-recipe, with additional optarg "-w | --with-identifiers"

Hey @timsutton,

I put this PR together after thinking about #133.
It extends the `../autopkg/list-recipe` functionality by allowing a `-w | --with-identifiers` optarg

```
$ /usr/local/bin/autopkg list-recipes --with-identifiers

Adium.download                           com.github.autopkg.download.Adium
Adium.munki                              com.github.autopkg.munki.Adium
Adium.pkg                                com.github.autopkg.pkg.Adium
AdobeAIR.pkg                             com.github.autopkg.pkg.AdobeAIR
AdobeAcrobatPro9Update.download          com.github.autopkg.download.AdobeAcrobatPro9Update
AdobeAcrobatPro9Update.munki             com.github.autopkg.munki.AdobeAcrobatPro9Update
AdobeAcrobatProXUpdate.download          com.github.autopkg.download.AdobeAcrobatProXUpdate
...

```
If no identifier is found for a recipe column 2 will be left empty.
Obviously if `-w` is left off, it will continue with current behavior.

I also removed some duplicate code by concatenation the match array for top level and one level down recipes.

Thanks for your consideration.
-- Eldon
Maybe we drop the `-x` short option and just leave `--plist`? I get that it's like "xml", but I can think of a lot of other CLI options that might start with `-x`.