Index: commits with conflicts not detected

[MarcusDenker]

When you have two transactions changing the same key, after we commit one, the second commit should be an errror.

This tests shows that currently, as expected, a new transaction sees the changes of "tx1 commit", but
the second commit raises no error:

testConcurrentAddKey2
	| tx1 tx2 tx3 |
	tx1 := soil newTransaction.
	tx1 root: dict.
	tx1 commit.
	
	tx1 := soil newTransaction.
	tx1 root
		at: #one put: #onevalue.
	tx2 := soil newTransaction.
	"We change the same key in tx2"
	tx2 root
		at: #one put: #twovalue.
	tx1 commit.
	tx2 commit. "the second should be error"
	
	tx3 := soil newTransaction.
	self assert: (tx3 root at: #one) equals: #onevalue.

testRemoveKeyWithTwoTransactions is a skipped test for the case of remove

[MarcusDenker]

Idea how to detect conflicts:

We already check every transaction log entry for every not commited transaction for restore, we could add to that.

• split restore in read vs. change (add, remove)
• when changing: check if any other transaction touches the same key / key-value in a "conflicting transactions" list
• on commit: if a conflicting transaction commited before us, fail.
• if commit possible: go over the conflicting list and add us to all the conflict list of all the transactions listed there