Fixes for updating indices, charset/collation and engine type on plugin-created tables.

Under MySQL, new tables will be created as InnoDB with UTF-8 (utf8/utf8_bin) same as core tables.
Existing plugin tables will have table engine and default charset/collation updated, and string columns will have charset updated, at checkschema time.

Switched from 'DESCRIBE' to INFORMATION_SCHEMA for pulling column information in order to get charset. A second hit to INFORMATION_SCHEMA is also needed to get table properties.

Indices were only being created at table creation time, which ain't so hot. Now also adding/dropping indices when they change.

Fixed up some schema defs in OStatus plugin that were a bit flaky, causing extra alter tables to be run.

TODO: Generalize this infrastructure a bit more up to base schema & pg schema classes.

plugins/OStatus/classes/FeedSub.php

@@ -110,7 +110,7 @@ class FeedSub extends Memcached_DataObject
                                    /*size*/ null,
                                    /*nullable*/ false,
                                    /*key*/ 'PRI',
-                                   /*default*/ '0',
+                                   /*default*/ null,
                                    /*extra*/ null,
                                    /*auto_increment*/ true),
                      new ColumnDef('uri', 'varchar',
@@ -450,3 +450,4 @@ class FeedSub extends Memcached_DataObject
     }
 
 }
+