Log Message:
Update to 1.20

Upstream changes:
1.20    2015-06-28

- Fixed a bug with stack handling in the XS code. If a callback sub caused
  Perl to reallocate the stack this could trigger weird errors of the form
  "Bizarre copy of ARRAY" from Perl itself. Fixed by Noel Maddy. GH #5.

- Fixed use of inlining in the XS code to work when "gcc -std=c89" is
  specified. Fixed by Vincent Pit. GH #6.

- Previously, Params::Validate would eagerly stringify all values it was
  validating, even though this stringification was only needed for error
  messages that are used when a parameter fails. For objects which overload
  stringification and do real work, this added an unnecessary
  slowdown. Stringification is now delayed until it is needed. Reported by
  Klaus. RT #105326.