core of a negative ineteger

[Max Alekseyev <maxale@gmail.com>]

I believe that core of a negative integer should return a negative
integer (that would match the definition of core). Currently the
result is always positive.
In particular, core(-1) should return -1 not 1 and core(-1,1) should
return [-1,1].
Don't you agree?

Currently we have:

? core(-1)
%1 = 1
? core(-1,1)
  ***   at top-level: core(-1,1)
  ***                 ^----------
  *** core: negative integer in sqrtint.

Regards,
Max