Write performance for large child node lists

[Michael Dürig]

Hi,
During my work on OAK-102 and OAK-106 I was eventually convinced by 
Jukka to switch from using a change log to accumulate transient changes 
to an approach where the change log is calculated from the resulting 
states instead. Now this seems to bite already. Witing large child node 
lists seems to be trouble some wrt. performance: since the comparison 
needs to iterate over ever more child nodes, writing child nodes does 
not scale in constant time any more but rather in time linear to the 
total number of child nodes. That is, adding the n-th node takes approx. 
n times as long than adding the first node did.

Michael