reports: date filters may not return full results

for example:

1. open the bookkeeping transaction report
2. set transaction date to "today"
3. run search and compare with transactions processed during the course of the day – many will be absent.

This is because in CRM_Report_Form::dateClause() we strip out the time value from dates, which means our date clause looks like:
WHERE ( trxn_date >= 20170214 ) AND ( trxn_date <= 20170214 )

Any transaction that happened during the day, aside from 12:00am, would be excluded from that query. The date clause should look like:
WHERE ( trxn_date >= 20170214 ) AND ( trxn_date <= 20170214235959 )

here is where the problem is (along with the lines below it for the $to value)
https://github.com/civicrm/civicrm-core/blob/master/CRM/Report/Form.php#L2021

interestingly, before that code is run, we call getFromTo(), which properly sets the correct $toTime. basically – we're doing the right thing by setting the $toTime and then immediately after are stripping it out.

the clause conditions on CRM_Utils_Type::T_DATE, but there's no equivalent type for T_DATETIME (there is T_TIME and T_TIMESTAMP, but neither handle the data the way we need it). so I think the question is – why do we strip out the time from the date clauses to begin with? I don't see the rationale behind why that was implemented.

I've marked this major, as it has the potentially to significantly affect reporting results that use date fields.