added tests for html-longdesc

See README.html for more info.
renamed files to follow manual test naming convention

Renamed all of the manual test files (not supporting files) with a -manual suffix to satisfy naming convention for manual tests.  Updates references in README.html.
Pretty-print messages.json so git-diff shows diffs
Test that 'directory' and 'mod' elements get the HTMLUnknownElement interface.
Merge pull request #399 from Ms2ger/unknown-elements

Test that 'directory' and 'mod' elements get the HTMLUnknownElement interface; r=zcorpan
Merge pull request #382 from cptvitamin/cptvitamin/html-longdesc

added tests for html-longdesc