Upgrade Scalar::Util from version 1.49 to 1.50

Upgrade Scalar::Util from version 1.49 to 1.50

[DELTA]

1.50 -- 2018-02-20 19:13:27
[CHANGES]
* Added head() and tail() functions (thanks preaction)
* Support binary and Unicode in symbol names for set_subname()

[BUGFIXES]
* Fix building with C++ and C89 compilers
* Fix uniq() test for old Test::More
* Fix example get_code_info for unnamed subs (RT#116962)
* Fixes for symbol names containing ' characters
* Don't leak SVs from sum0/product1 when called with zero args (RT#124017)
* Use sv_rvunweaken() in Scalar::Util::unweaken() (thanks ilmari)
* Misc. fixes for perl 5.6