extensionFromMime 'audio/mpeg' returns 'mpga' instead of 'mp3'

[fstotz]

When using extensionFromMime for 'audio/mpeg' the returned type is 'mpga' instead of 'mp3'.
On IOS trying to play back a .mpga file it fails.
When using .mp3 it works fine.

[lrhn]

Different mime.types files seem to have either mpga or mp3 as first extension for audio/mpeg.

Apache has mpga: https://svn.apache.org/repos/asf/httpd/httpd/trunk/docs/conf/mime.types

Maybe the order isn't significant, and we should have a separate registry of "preferred extension" that we can use instead of defaulting to the first one in the list.