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
add parameter at($DATE_AT) and mind revisions
Improved isCurrentRevision(), tests included
refactor PageRevisionLog into Media- and PageChangelog extending Changelog
fix not updated call, renaming