Optionally process full-text queries with InnoDB FTS

(See also: http://wiki.civicrm.org/confluence/display/CRM/Full+Text+Search )

1. Implement a class, CRM_Core_InnoDBIndexer, which can:

1a. Add FTS indices to specific list of tables/columns

1b. Drop all FTS indices

1c. Reindex (ie drop + recreate all indices)

2. Add a setting, "enable_innodb_fts". Changes to the setting should trigger InnoDBIndexer.

3. Expose the setting in the admin UI.

4. Update the FullText search classes:

4a. When "enable_innodb_fts" is false, use the same queries we currently use. The basic conditional in each query should be "col1 LIKE '%query%' OR col2 LIKE '%query%'"

4b. When "enable_innodb_fts" is true, use the same overall query structure, but change basic conditional to "MATCH(col1,col2) AGAINST ('query')"

5. When upgrading, display warnings if "enable_innodb_fts" is active. Sysadmins may need to reindex.