Refactor/improve <tag> support.
* build/targets.jam (generate-realy):
After applying tag, we used to 'temporary' change self.name,
which is horrible. How pass the name to 'construct'.
(construct): New parameter 'name'.
(tag-name): New rule, extracted from basic-target. This needs to be
separate rule so that we can call it from 'stage'. Check for a value of
from '@something' and interpret 'something' as a rule which returns the
new name.
[SVN r26408]
Vladimir Prus