[Bug #19426] Fix endless `Range#step` with `#succ` method

	Fix regression when testing inclusion in unbounded ranges

	Caused by 04a92a6764bf678919cf4b68a27496a39d6b886a.  This treats
	unbounded ranges of arbitrary objects the same as how unbounded
	string ranges are treated:

	  (..x)  === y  # (y <=> x) <= 0
	  (...x) === y  # (y <=> x) <  0
	  (x..)  === y  # (x <=> y) <= 0

	Fixes [Bug #19864]
	---
	 range.c                 |  9 +++++++++
	 test/ruby/test_range.rb | 23 +++++++++++++++++++++++
	 2 files changed, 32 insertions(+)

	Extract range type check functions

	---
	 range.c | 55 ++++++++++++++++++++++++++++++++++++-------------------
	 1 file changed, 36 insertions(+), 19 deletions(-)

	[Bug #19533] Fix infinite range inclusion with numeric value

	---
	 range.c                 | 10 +++++++---
	 test/ruby/test_range.rb |  2 ++
	 2 files changed, 9 insertions(+), 3 deletions(-)

	[Bug #19533] Add spec of infinite range inclusion

	---
	 spec/ruby/core/range/case_compare_spec.rb | 6 ++++++
	 1 file changed, 6 insertions(+)

Beginless ranges previously raised TypeError for this case,
except for string ranges, which had unexpected behavior:

  ('a'..'z').include?('ww') # false
  (..'z').include?('ww') # previously true, now TypeError

Use of include? with endless ranges could previously result
in an infinite loop.

This splits off a range_string_cover_internal function from
range_include_internal.

Fixes [Bug #18580]

Fixes [Bug #18983]

Previously `(2..).cover?("2"..)` was false, but
`(..2).cover?(.."2")` was true.  This changes it so both are false,
treating beginless ranges the same as endless ranges in regards to
type checks.

This also adds documentation to #cover? to describe behavior with
beginless and endless ranges, testing each documentation example,
which is how this bug was found.

Fixes [Bug #18155]

Previously, include? would return true for the end of the range,
when it should return false because the range is exclusive.

Research and Analysis by Victor Shepelev.

Fixes [Bug #18577]

* numeric.c: prohibit zero step in Numeric#step

* range.c: prohibit zero step in Range#step

* Fix ruby-spec

[Feature #15573]

Matz want to try to freeze all Range objects.
[Feature #15504]

Reverted in e080a4cdee