[perl #130439] [REGRESSION] splice no longer attempts to numify things (@a.splice: ^3)

[Zoffix Znet via RT]

The original fix was reverted in 
https://github.com/rakudo/rakudo/commit/121e5e32e9 per discussion 
https://irclog.perlgeek.de/perl6-dev/2017-01-21#i_13962511