copy/paste: try to convert geometries
added test for QgsGeometry::convertToType
do not convert multiline to multipolygon if one of the part failed, also consider case of 3 vertices line with first and last vertex identical
copy/paste: do not transform if layer has unknown geometry
Merge pull request #1120 from 3nids/pasteconvertgeom

copy/paste: try to convert geometries (fixes #3604)