Added diff navigation
 Navigation links to move to previous edit before revision in left column or next/last edit after revision in right column.
Add working EoF and BoF checks when chunck reading.
Also isset on meta-last_change-date entry.
Add some breaks to while loops.
some refactoring
merge master in branch
Wrap thead around 1st row, when 1st cell at 1st row is tableheader. Implements FS#1764
add <THEAD> to top rows of tables when all cells are <TH>
update tests for use with <THEAD> changes
swap order ot test parameters to match expected,actual as per documentation & test output
Merge pull request #390 from splitbrain/tablethead_chris

multi-row THEAD & tests
Merge remote-tracking branch 'origin/master' into diff_navigation
page related changelog reading refactored to class
Update changelog unit tests
Add unit tests for getRelativerevision
update function calls to changelog functions
isCurrentPage is page dependent
Improved isCurrentRevision(), tests included
refactor PageRevisionLog into Media- and PageChangelog extending Changelog
fix not updated call, renaming
improve unittests getrelativerevision. Bit code reformatting unit tests