[src/core/Range.pm] allow *..*

It now means -Inf .. Inf.

See the following resources for rationale:

- http://irclog.perlgeek.de/perl6/2014-08-30#i_9271208 (until 16:41)
- spec:cba89c2537d100be8fac3a5d13200671afd3243f
- roast:782fee4de0817a1950d7d4744f0a45f3836e7d3d