Drush should not merge together aliases with the same name

Removing #hidden was dubious. I'm going to work on this some more.

Here is a patch with better handling of multiple matches than before. If you attempt to use '@dev' when multiple aliases files contain aliases that match that name, you will now get an "ambiguous result" warning followed by a "no alias matched" error. This avoids the rather large problem that can be caused by the current technique of merging unrelated alias records together.

If you wish to operate on multiple aliases, the 'all' groupname can be used; e.g.: drush @all.dev status will display status for all '@dev' aliases. It is also possible to leave off the group name from the alias if drush can infer which group is intended by way of the other aliases used in the same command; e.g.: drush sql-sync @site.live @dev will prefer @site.dev if it can be found.

All tests pass; if the code looks good, I'll update up the docs and add a change notification.

Here is the missing patch. I could remove the feature mentioned in #3 if desired, but it is important to replace the current record-merging behavior with something more reasonable. Hopefully most of this patch will be acceptable.

I had an idea to make this feature more explicit that would only take a little bit of code to implement.

"@related." === the same group as another alias in use:

drush @site.dev site-alias @related.live === drush site-alias @site.live

drush rsync @site.dev @related.live === drush rsync @site.dev @site.live

To shorten typing this, "@." === "@related.":

drush rsync @site.dev @.live === drush rsync @site.dev @site.live

The main use of this, though, is not the nominal usefulness of reducing typing on the cli, but to make scripts and shell aliases more flexible. For example:

$options['shell-aliases']['pull-data'] = '!drush sql-sync @related.live {{@target}} && drush rsync @related.live:%files {{@target}}:%files'

Usage:

drush @site.dev pull-data

With just a touch more work, {{@target}} could probably become @self. With a few useful examples in drush topic docs-shell-aliases, it wouldn't be too hard for folks to create customized workflows the pull from live or stage or wherever is appropriate for their dev environment.

If this looks good, I'll roll a new patch.

Here is a patch that supports the constructs described #5; it is nearly the same as #4.

Here is a fix for multiple match handling that does not add any well-known-groupname magic. All tests pass.

Committed.

Forgot to set status.