Correctly handle large negative usec value.

Change AppVeyor's clone_depth

This reverts commit 6dabb336.

Change return value of Enumerable#each_slice

Change return value of Enumberable#each_cons

More compatibility to CRuby.

More compatibility to CRuby.

Note this is a temporary fix. Error message generation
(including `inspect`) should be deferred until its use.

Fix parameters when noname rest

According to CRuby [Feature#12746]

Modify to get constant of parent module in singleton class; fix #3568

The resulting behavior is different from CRuby, but modifying
hash key afterwards is undefined behavior in ISO spec.