Flags for ST_IsValid*

[strk]

Allow ST_IsValid (and friends) to take flags driving run. In particular, we'll want to allow exposing the SelfTouchingRingFormingHoleValid flag.

See ​http://geos.osgeo.org/doxygen/classgeos_1_1operation_1_1valid_1_1IsValidOp.html#402a7a6cedd2e50c83977d8fe2afc39e

[strk]

As of r6826 the flag is allowed in ST_IsValidDetail. Since that function is already new, and requiring GEOS 3.3.0 I tought it'd be useful to have the flag there.

Now, if we also want to have support in the other two (ST_isValid and ST_isValidReason) we'll need to switch implementation based on GEOS version, with the pre-geos-3.3 implementation raising an exception if a flag != 0 is given.

Do you think it's worth it ?

[strk]

I've resolved to add 2 signatures for ST_isValid(geom,int) and ST_isValidReason(geom,int) which are _only_ given when building againts GEOS-3.3 or up and are implemented as simple wrappers to ST_isValidDetail.

Will commit with documentation and testing.

[strk]

Done with r6828