A small gotcha and a proposed fix

[goran at krampe.se]

Hi Chris and folks!

With the current implementation of MagmaSession>>commit: you can make an
"early exit" and miss the actual commit like this:

session commit: [
	^mObject foo: 3]

Which will set foo to 3 and then return the result of that -
unfortunately missing the actual commit in MagmaSession>>commit: since
that code looks like this:

commit: aBlock

	| result |
	self begin.
	result := aBlock value.
	self commit.
	^result
 
Since Magma "supports" nested transactions (it just keeps a nest level
count and the actual commit occurs when you are all the way back out -
so it all turns into a BIG commit - fair enough) the effect is that you
now are one level down and subsequent calls to commit: will of course
not do anything. And yes - it was a bit painful to figure that stupid
thing out. :)

Better would probably be:

commit: aBlock

	self begin.
	^[aBlock value]
		ensure: [self commit]

If there is an error in "self begin" we don't try to commit but if
"aBlock value" returns we don't miss the commit.

regards, Göran