Add some humanistic logic to test time precision.

Precision should really be a function of the number of tests and time. A
small number of tests with a long time, does not warrant a high
precision. However, if you had 8,000 tests (think JPL code) you would
care about a higher precision, even if your test suite ran for 4
minutes.

Since the code that does the formatting does not know about the number
of tests, the following is a rough middle ground, which is completely
arbitrary based on how I felt and not on any real science.

  * <   1 seconds: Give me all the precisions
  * < 120 seconds: Hundredths of a second are good
  * < 300 seconds: Tenths of a second, because I just can't give em up
  * > 300 seconds: Seconds, because you can't wait this long anyways

[Close #807]
Merge pull request #833 from cupakromer/sane-execution-pericision

Add some humanistic logic to test time precision.
Move the 2 enhancements that were listed under 2.13.1 into dev section.

They haven't been released yet (patch releases shouldn't contain new
features), and were erroneously added to the 2.13.1 section.
Address deprecation warning from rspec-mocks.
Prevent an inner group method def from overriding an outer group subject.
Merge pull request #814 from rspec/prevent_invalid_named_subject_override

Prevent an inner group method def from overriding an outer group subject
added test for random number generation
replace rand generation with instance of Random
Revert "replace rand generation with instance of Random"

This reverts commit 66b14a919f111cf0b8feb1f08485f098e9c14025.
reset seed after ordering
Synchronize `rspec spec` and `rake spec` output

By removing the `rake spec` short circuiting the output between
invocation methods matches more closely.

Fixes rspec/rspec-core#812
Update docs to warn against using let/subject in `before(:all)`.
Revert "added test for random number generation"

This reverts commit 4b46c9b2d071f2416f627fad8a76b090bc99f8e6.
added test created by @myronmarston
Merge pull request #837 from mshytikov/rand

Replace Kernel.srand with Random.new
Fix indentation.
Changelog entry for #837.

[ci skip]
cleanup white space
Pending spec for shared context that exposes Issue #632
revert whitespace cleanup in console output (doh)