demandimport: enforce ignore list while processing modules in fromlist
If a module is loaded as "from . import x" form, there has been no way to
disable demand loading for that module because name is ''. This patch makes
it possible to prevent demand loading by '<package-name>.x'.
We don't use _hgextimport(_origimport) here since attr is known to be a
sub-module name. Adding hgext_ to attr wouldn't make sense.
http://example.com/no/anchor, branches: (None, [])
http://example.com/an/anchor, branches: ('foo', [])
http://example.com/no/anchor/branches, branches: (None, ['foo'])
http://example.com/an/anchor/branches, branches: ('bar', ['foo'])
http://example.com/an/anchor/branches-None, branches: ('foo', [])
http://example.com/, branches: (None, [])
http://example.com/, branches: (None, [])
http://example.com/, branches: ('foo', [])