[Bug #20654]

This commit fixes Integer#ceil and Float#ceil when the number is
negative and ndigits is large such that 10**ndigits is a bignum.

Previously, it would return 0 in such cases. However, this would cause
unexpected behaviour such as:

    puts 1.ceil(-5) # => 100000
    puts 1.ceil(-10) # => 10000000000
    puts 1.ceil(-20) # => 0

This commit changes the last result so that it will return
100000000000000000000.

[Bug #20654]

This commit fixes Integer#floor and Float#floor when the number is
negative and ndigits is large such that 10**ndigits is a bignum.

Previously, it would return 0 in such cases. However, this would cause
unexpected behaviour such as:

    puts -1.floor(-5) # => -100000
    puts -1.floor(-10) # => -10000000000
    puts -1.floor(-20) # => 0

This commit changes the last result so that it will return
-100000000000000000000.

	[Bug#19445] Fix keyword splat in enumerator

	Extracted arguments do not have keyword hash to splat.
	---
	 numeric.c                 | 2 +-
	 test/ruby/test_numeric.rb | 3 +++
	 2 files changed, 4 insertions(+), 1 deletion(-)

This patch is suggested by nobu.

Benchmark result:

```
require 'benchmark'

n = 10 ** 7

Benchmark.bm do |x|
  x.report("Fixnum/Fixnum") { a, b = 5, 2; n.times { a.ceildiv(b) } }
  x.report("Bignum/Bignum") { a, b = 10**100, 10**99 - 1; n.times { a.ceildiv(b) } }
  x.report("Bignum/Fixnum") { a, b = 10**100, 3; n.times { a.ceildiv(b) } }
end
```

Original:

```
       user     system      total        real
Fixnum/Fixnum  3.340009   0.043029   3.383038 (  3.384022)
Bignum/Bignum  8.229500   0.118543   8.348043 (  8.349574)
Bignum/Fixnum  8.328971   0.097842   8.426813 (  8.426952)
```

Improved:

```
       user     system      total        real
Fixnum/Fixnum  0.699140   0.000961   0.700101 (  0.700199)
Bignum/Bignum  5.076165   0.083160   5.159325 (  5.159360)
Bignum/Fixnum  5.548684   0.115372   5.664056 (  5.666735)
```

[Misc #18891]