merge revision(s) 254bed30,fad3023e,3156fb0f: [Backport #17218]

	Renamed `nurat_sub` compliant with `rb_rational_plus`

	---
	 internal/rational.h | 1 +
	 rational.c          | 6 +++---
	 2 files changed, 4 insertions(+), 3 deletions(-)

	Fix ArithmeticSequence#last and ArithmeticSequence#each for
	 non-integer sequences (#3870)

	[Bug #17218]
	[ruby-core:100312]
	---
	 common.mk                             |  2 +
	 enumerator.c                          | 99 ++++++++++++++++++++++++++++++++---
	 internal/numeric.h                    |  2 +
	 internal/rational.h                   |  2 +
	 numeric.c                             | 53 ++++++++++---------
	 rational.c                            | 28 +++++++---
	 test/ruby/test_arithmetic_sequence.rb | 10 ++++
	 7 files changed, 156 insertions(+), 40 deletions(-)

	test/ruby/test_arithmetic_sequence.rb: remove a duplicated test

	There is another "test_last_bug17218"
	---
	 test/ruby/test_arithmetic_sequence.rb | 5 -----
	 1 file changed, 5 deletions(-)