This commit adds two new methods to the `Math` module:

* `Math.log1p(x)`: Computes `Math.log(x + 1)`
* `Math.expm1(x)`: Computes `Math.exp(x) - 1`

These methods are often more accurate than the straightforward
computation, especially when `x` is close to zero.
The corresponding functions, `log1p` and `expm1`, are defined in the C99
standard math library.

[Feature #21527]

This should return 0, but on glibc it returned NaN.

Fixes [Bug #17804]

* math.c (math_cbrt): refine the approximation result on boundary
  values by an iteration of Newton-Raphson method.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63592 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

* math.c (tanh): check overflows, and return +-1.0.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55798 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

* object.c, numeric.c, enum.c, ext/-test-/bignum/mul.c,
  lib/rexml/quickpath.rb, lib/rexml/text.rb, lib/rexml/xpath_parser.rb,
  lib/rubygems/specification.rb, lib/uri/generic.rb,
  bootstraptest/test_eval.rb, basictest/test.rb,
  test/-ext-/bignum/test_big2str.rb, test/-ext-/bignum/test_div.rb,
  test/-ext-/bignum/test_mul.rb, test/-ext-/bignum/test_str2big.rb,
  test/csv/test_data_converters.rb, test/date/test_date.rb,
  test/json/test_json_generate.rb, test/minitest/test_minitest_mock.rb,
  test/openssl/test_cipher.rb, test/rexml/test_jaxen.rb,
  test/ruby/test_array.rb, test/ruby/test_basicinstructions.rb,
  test/ruby/test_bignum.rb, test/ruby/test_case.rb,
  test/ruby/test_class.rb, test/ruby/test_complex.rb,
  test/ruby/test_enum.rb, test/ruby/test_eval.rb,
  test/ruby/test_iseq.rb, test/ruby/test_literal.rb,
  test/ruby/test_math.rb, test/ruby/test_module.rb,
  test/ruby/test_numeric.rb, test/ruby/test_range.rb,
  test/ruby/test_rational.rb, test/ruby/test_refinement.rb,
  test/ruby/test_rubyvm.rb, test/ruby/test_struct.rb,
  test/ruby/test_variable.rb, test/rubygems/test_gem_specification.rb,
  test/thread/test_queue.rb: Use Integer instead of Fixnum and Bignum.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55029 b2dd03c8-39d4-4d8f-98ff-823fe69b080e