As per my email to postgis-devel, this commit contains a major reworking
of the inner core, with many bugfixes. The primary changes are:

- Elimination of FILENODE, since we can just use pointers to
  SHPLOADERCONFIG

- Abstract the configuration structures from the GUI interface

- Restrict entry to either drag/drop or file chooser

- Instead of constantly destroying/creating new dialogs, create
  them once and then just show/hide them (in particular this
  enables the file chooser to open at its previous directory)

- Add separate connection details and progress bar dialogs

- Rework both internals and GUI in preparation for adding dumper
  support

Note that the dumper integration changes are being worked on separately
and will be included in a later commit.

git-svn-id: http://svn.osgeo.org/postgis/trunk@8706 b70326c6-7e19-0410-871a-916f4a2858ee