Add specs for recursion guard on `<=>`

This adds specs to Time and String to ensure that the reverse comparison
they perform as part of the `<=>` method does not result in a stack
overflow. Related to [Ruby Bug
test suite (for the specific case of comparing a Time object to a String
object)
[here](https://github.com/ruby/ruby/blob/trunk/test/ruby/test_comparable.rb#L73)
Update wording for spec
Remove unnecessary "should not raise" check
Merge pull request #263 from jballanc/invcmp-spec

Add specs for recursion guard on `<=>`
Fixed the 'loads an array having an ivar' spec for Marshal.load.  In Ruby, Array#== and String#== do not consider the instance variables so the test was not actually testing them.
Removed ruby_version_is guards from Array specs.
Added specs for Enumerator#peek behaviour. When the Enumerator position is already at the end and method peek is called.
Merge pull request #266 from lucasallan/enumerator-peek

Added specs for Enumerator#peek behaviour.
Revert "Added specs for Enumerator#peek behaviour. When the Enumerator position is already at the end and method peek is called."

This reverts commit 1728b8bcfd826e9105270d1ffa26a59724c250e0.

There's an existing spec for this:

https://github.com/rubyspec/rubyspec/blob/master/core/enumerator/peek_spec.rb#L33-36
Merge pull request #265 from DavidEGrayson/pull_request_1

Fixed the 'loads an array having an ivar' spec for Marshal.load
Fix a spec typo for Exception#set_backtrace
Add Exception#set_backtrace specs for weird arguments
Fix a sharing spec for Module#public with eval
Added specs for Module#const_get with '::A::B'.
Add spec for rb_fd_fix_cloexec
Add spec for opening file with text mode
Add missing fixture file
Added specs for String#to_i with bases.
Added more Integer() specs.
Add specs for rb_intern_str to C-API