MDL-21029 glossary - fix display of entries belonging to site/course global glossaries ; merged from 19_STABLE

portfolio/leap2a MDL-21036 & MDL-21034 : use proper date format in leap2a, and updated forum to use it

"MDL-20125, added configurable setting to section_links block, credits to Jason Hardin, merged from 1.9"

"MDL-20819, sometimes, modules return non-array which can break stats processing, added more error checking, merged from 1.9"

This commit includes:

- leap2a portfolio format, and xml writer
- proof of concept implementation in forum and assignment modules
- a lot of refactoring of the portfolio formats in general:
    - addition of "abstract" formats - this is necessary for plugins to be able to support groups of formats
    - addition of the idea of portfolio formats conflicting with eachother - eg richhtml & plainhtml

it touches modules other than assignment and forum, because the format api
changed and now each place in moodle that exports portfolio content has to deal
with the formats it supports slightly differently.

At the moment the Mahara portfolio still doesn't support this format, because I
haven't done the Mahara side yet. The "file download" plugin supports it
though.

Still todo:

- Add support for the other places in Moodle (glossary, data, etc)
- Write tests, once the rest of the portfolio tests have been updated to use the new DB mocking stuff
- Fix a bunch of TODOs

MDL-2684: kses strips out CSS from style tags unless the first property is on 'allowed' list, this is silly

flash upgrader MDL-20841 New config setting excludeoldflashclients will set a minimum version for flash clients. A check in the standard_head_html is run once, and will set a session variable with the current flash version. If the current flash version is lower than the minimum requirement, then Moodle will serve alternate content whenever a flash file is requested. The alternate file will ask the user to upgrade flash, merged from 1.9

Example: Yay, grade tests 40 mins down to 50 secs!

method. 100x speedup for UnitTestCaseUsingDatabase tests. Defaults to false (old behaviour)