test-revert: put content, not keys, into 'combination'
By putting the file content rather than keys in the 'combination'
list, we restrict the knowledge of 'ctxcontent' and 'wccontent' to the
loop generating the combinations. That will make it easier to replace
the generation code.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.