Add issue on last revision

[blabno]

Often I'm editing some files and find out that there is a piece of code worth reporting QA issue. This is however too late to mark the code because the file has been already modified.

It would be very useful for such occassions to be able to popup a view of the file's original content from current revision. We could reuse "Compare with the same repository version" screen or create a new one (i.e. read-only editor window).