wp_bp_activity stores item_id and secondary_item_id as VARCHAR; breaks indexes

[boonebgorges]

The item_id and secondary_item_id columns in wp_bp_activity are varchar(75). This is bad in a couple of ways:

• When querying on a specific item/secondary item, our query class casts the items to int (in clauses like WHERE a.item_id IN ( 5,8,20 )). The type mismatch between our query and the column means that MySQL can't use its indexes and has to do a full tablescan.
• varchar is less efficient when an integer type would work
• We're casting to int before writing to the activity table anyway

Should just be able to change the table definition and let dbDelta() do its work, but this will need some testing.

[boonebgorges]

4104.01.diff changes the schema and bumps the db number to prompt an upgrade. Looks good on my local, but I would like a second opinion before committing.

[DJPaul]

Looks good here.

[DJPaul]

I'm going to commit this on your behalf so we can get it tested from people running trunk. It seems solid from my testing.

[djpaul]

(In [5955]) Correct item_id column types in activity table schema. All props to boonebgorges, fixes #4104

[johnjamesjacoby]

Confirmed. Looks good to me. Nice work.