Cleaned up test structure and messages

• Broke down each test into bracketed steps, each prefixed by the constants it uses (that are sometimes referenced later on) and the name of the step in the form of a NSString set to a new `test_step` ivar.
	• All assert messages now start with “After %@” with “%@” filled in with the `test_step`.  The “at this point” suffixes eliminated.
• Some of the assert messages improved to “_underline_” the most critical part of the message (namely, an easily-confusable state descriptor).
• All assert messages are now sentence-case and end with a period, which should make them stand out better.
• `P001ModelSurrogate` instances are now allocated to autorelease (which happens at the end of the test because SenTest has every test invoke wrapped in `[[NSAutoreleasePool alloc] init]` and `[pool release]`.