Error reporting in makeCopySqlite

[wonder-sk]

A couple of related issues:

 - error from sqlite is not passed to the exception -> no detailed info when exception is raised
 - Sqlite3Db::create() should provide more info about the error
 - GEODIFF_makeCopySqlite() does not say what is the problem when opening/creating
 - GEODIFF_makeCopySqlite() should report if it deletes a DB file (and if it was successful)
 - GEODIFF_makeCopySqlite() should maybe first try to open it as SQLite, only then remove it