Revert "Remove useless optimizations from the ContextPart"

Paolo writes:
The point is not to optimize #ip and #sp.  It is to _prevent_
optimizing it, and ensure that the cached values are committed
by the interpreter to the object before reading the variable.

This reverts commit 427e48633bdffb03a8934675616ba2eea63ff19d.

2013-06-27  Holger Hans Peter Freyther  <holger@moiji-mobile.com>

	* kernel/ContextPart.st: Revert the previous change.
sunit: Add >>#assert:equals: from Pharo for the Phexample

The above selector is needed for Phexample and in general very
nice to debug failures as the result and expectation is immediately
visible in the debugger.

2013-05-11  Holger Hans Peter Freyther  <holger@freyther.de>

	* packages/sunit/SUnit.st: Add #assert:equals: and
	#comparingStringBetween:and: from Pharo to the TestCase.