Negative distance argument to ST_Buffer not documented

[rutsky]

Documentation to ST_Buffer [1] says that argument "radius_of_buffer" is distance and defines buffer operation as "all points whose distance from this Geometry/geography is less than or equal to distance".

Documentation implies that ST_Buffer can buffer only on positive values which isn't correct as I see in practice, and since ST_Buffer is implemented using GEOS it is possible to buffer on negative distances [2].

[1] ​http://www.postgis.org/docs/ST_Buffer.html

[2] ​http://geos.refractions.net/ro/doxygen_docs/html/classgeos_1_1operation_1_1buffer_1_1BufferOp.html

[pramsey]

1.5 branch at r9207

2.0 at r9208