Fix naming issues in writeOGR.

Also includes a conversion of factors to characters, as ordered factors cause writeOGR to fail (and all other factors are converted to character anyway)
Add to Rbuildignore
Merge branch 'master' into spdf_geojson_fix

Conflicts:
	.Rbuildignore
Simplify SpatialPolygonsDataFrame_togeojson
Use path.expand
Merge pull request #8 from ateucher/spdf_geojson_fix

Fix path issues with SpatialPolygonsDataFrame_togeojson