Makes the command name be steal-tools

```js
steal-tools build
```

```js
steal-tools pluginify
```

Addresses problem discussed in #45
bin/steal should user pluginifier

stealTools.pluginify was renamed to stealTools.pluginifier so this
updates the command-line script to use that.
Merge pull request #46 from matthewp/command-name

Makes the command name be steal-tools
Allow callback to be optional with pluginify

This fixes the shim to make the callback argument to be optional. For
example, this is valid steal:

```js
steal('can', 'app');
```

Fixes #31
Merge pull request #31 from matthewp/no-callback

Pluginify shim should allow callback to be optional
Prevent swallowing of errors

Previously we were swallowing errors that occurred during the
multi-build process. This adds a test of what happens when we try to
load a module that doesn't exist. The result should be that the promise
is rejected, bubbling all the way up to the user. This fixes it. Fixes
Merge pull request #64 from matthewp/errors

Prevent swallowing of errors
Exclude plugins for global pluginified files

This adds an option to concatSource to allow the exclusion of plugins
from the bundle.source. This is necessary because o plugins that are not
meant to be included in the build, a `System.set` call is added which
will not work for global pluginified outputs. Fixes #42