sql_ilike() refactoring

sql_ilike() is the only remaining function that returns one string (the ilike operator) instead of one SQL fragment. We have already changed some old helper sql functions to return SQL fragments and I think it would be great to do the same with this function. In fact we are going to need it because to implement support for ilike() in Oracle, I need to call some Oracle functions, so I propose to do:

function sql_ilike($fieldname)

where fieldname can be one fieldname or one placeholder, np with that.

Requires:

• implement the new function.
• change all old uses
• modify tests

Thoughts?