Second try at delimited text fix

As per previous pull request, fix for delimited text provider including proper handling of new lines in quoted fields, files without header records, selection of geometry type (point,line,polygon) in WKT files with mixed geometries, better error handling, handling of coordinates in degrees/minutes/seconds.  Gui changes to provider plugin to support changed feature set, also to make initial selection of wkt and xy fields more intelligent, and saving of file type specific options for delimiters etc.  Nearly comprehensive test cases for provider(!?).  Doxygen formatted documentation of this and other vector providers in qgsvectorlayer.h.  Thanks to Jeremy Palmer for text of WFS provider.