Fix crash when another subclass of XCTestObserver is injected

This fixes the crash when another subclass of XCTestObserver is
injected.

Such as:
* https://github.com/tokorom/GenerateTestCoverageFor_iOS7/blob/0.1.0/GenerateTestCoverageFor_iOS7/TKRGcovFluserTestObserver.h
* https://github.com/jonreid/google-toolbox-for-mac/blob/2981e05/UnitTesting/GTMCodeCoverageTestsXC.m

XCTestObserver allows us to use multiple test observers at the same time
by setting the XCTestObserverClass user default (See XCTestObserver.h).
So we need to ensure that the method swizzling by Specta won't crash
another observer.

Originally -startObserving is defined by Apple on XCTestObserver, which
is the superclass of XCTestLog. However, in Specta, we define
-spt_shouldProxyToSPTReporter on XCTestLog and calling it in
the swizzled -startObserving.
Thus, if -startObserving of a *direct subclass* of XCTestObserver
(i.e. not a subclass of XCTestLog) is invoked, the object does not
respond to -spt_shouldProxyToSPTReporter and it crashes.

This change fixes the crash by defining and swizzling the methods in
XCTestObserver instead of XCTestLog.
Execute `afterAll` despite pending examples.

Example groups would only execute `afterAll` blocks when the number of run
examples was equal to the total number of examples. Pending examples are
never run, so this condition was never met for example groups containing
pending examples.

Add `pendingExampleCount` and change condition to execute `afterAll`
blocks when `(ran + pending) = total`. Execute `afterAll` blocks whether
the example group contains pending examples or not.

Also add a test which fails without the new conditional, but passes when
the new conditional is used.

Note that `beforeAll` and `afterAll` blocks are *not* executed when all
examples in the group are pending. This is not consistent with RSpec
behavior, which executes `before(:all)` and `after(:all)` blocks even if
all examples in the group are pending (as of 3.0.0).

Addresses https://github.com/specta/specta/issues/61.
Merge pull request #63 from yujinakayama/fix-crash-with-multiple-observer

Fix crash when another subclass of XCTestObserver is injected
Add a Test configuration

This is especially useful for sandboxed apps so they can disable code
signing for tests.
Merge pull request #70 from mdiep/test-configuration

Add a Test configuration
Merge pull request #67 from modocache/61-execute-after-all-despite-pending

Execute `afterAll` despite pending examples.