The Ruby bindings were missing a way to get all the tags of the
database. Now you should be able to access this with the public
instance method `all_tags` of your database object.
Example of use:
notmuchdb = Notmuch::Database.new path, { :create => false,
:mode => Notmuch::MODE_READ_ONLY }
my_tags = notmuchdb.all_tags
my_tags.each { |tag|
print tag
}
my_tags.destroy!
Amended by db: improve error reporting, add test