MDL-24694 fixing broken upgrade once more - this step was skipped because two blocks had the same version number

assignment MDL-24694 added contexturl and contexturlname properties to email_teachers() message object.

- added message provider to manage assignment's messaging
- user_preferences.name length changed form 50 to 255 due to long messaging preference names.

community block MDL-24830 better "wait for upload" message + fix a javascript issue when screenshot number = 0 (metadata page)

global search MDL-24625 fixed up global search regressions so that indexing will complete successfully.

MDL-24852 latest YUI 2.8.1, unfortunately there is no support for it in yui phploader - that means we can not use it yet in moodle

MDL-24837 improved user preferences internal implementation, general code cleanup, minor bugfixing, fixed '0' value regression and improved caching options in cron scripts (this should hopefully help with messaging performance in cron once it is used there), implemented basic unit tests for user user preferences

Thanks to Derek Woolhead for the fix.

Fix thanks to Colin Chambers.

Thanks to Colin Chambers.

list-blocks MDL-24517 Altered class on list block contents so that bullet points aren't added (1.9 functionality)

image gallery MDL-24773 replace external image gallery library calls with a new image gallery created in community block

MDL-24523 adding note that clean_text() is designed to work with htm ltext only, technically we can not clean other formats before the conversion, sorry