Review Request: VcsEventWidget: Fetch only the last n events from the history, request earlier ones as needed

[Fabian Wiesel]

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http://reviewboard.kde.org/r/2638/
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Review request for KDevelop and Andreas Pakulat.


Summary
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VcsEventModel now has a IBasicVersionControl, so that it can fetch the events as they are requested by the view.
While it now supports the canFetchMore()/fetchMore() interface of QAbstractItemModel, further elements would
only be requested, if the bottom has been reached.
To hide the latency of fetching further events, they are internally prefetched, when a low watermark is reached.
The fields of the elements, which are currently fetched are returned by the model as "Loading...", so that the user
gets a feedback, that those fields are not yet available.

It relies on the following properties, which are not specified by the IBasicVersionControl::log() in that way,
but happens to be the case with the svn-plugin and (after that patch to DVcsJob) the hg-plugin.
- log() returns _at least_ "limit" events, or there are fewer events left than requested. This is required,
   so that the model can answer canFetchMore() correctly, requires only an update of the specification of log().
- finished() is fired _after_ resultsReady() (patch toDVcsJob)

VcsEventWidget also works directly with IBasicVersionControl, instead indirectly by getting it from the job.

Finally, only indirectly related, some const correctess in VcsEvent.


Diffs
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  /trunk/extragear/sdk/kdevplatform/vcs/dvcs/dvcsjob.cpp 1075986 
  /trunk/extragear/sdk/kdevplatform/vcs/models/vcseventmodel.h 1075986 
  /trunk/extragear/sdk/kdevplatform/vcs/models/vcseventmodel.cpp 1075986 
  /trunk/extragear/sdk/kdevplatform/vcs/vcsevent.h 1075986 
  /trunk/extragear/sdk/kdevplatform/vcs/vcsevent.cpp 1075986 
  /trunk/extragear/sdk/kdevplatform/vcs/vcspluginhelper.cpp 1075986 
  /trunk/extragear/sdk/kdevplatform/vcs/widgets/vcseventwidget.h 1075986 
  /trunk/extragear/sdk/kdevplatform/vcs/widgets/vcseventwidget.cpp 1075986 

Diff: http://reviewboard.kde.org/r/2638/diff


Testing
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Thanks,

Fabian