CRM-12432 make split out the extracting of where functions from the construction of the where clause
CRM-12432 allow filters to be marked to be skipped by the where clause constructor
De-hack additional operators being added for report class only

The buildDate range function is called about 20 times with no additional
operators being added & twice with them being added. But the default
behaviour was to add them. This makes the default behaviour NOT to add
them & makes the one class that does add them take responsibility for
passing them in rather than a round about method of deriving them
Merge pull request #691 from eileenmcnaughton/datefn

CRM-12053 rationalisation of datefilter functions

Note: I tested this locally earlier today and seems to fix the problems w/ search forms.