All char, char *, and char arrays changed to use wxChar or wxString. 99% backward...

All char, char *, and char arrays changed to use wxChar or wxString.  99% backward compatability maintained
Cleaned up code to remove duplicate blocks from multiple functions
Added better handling of failed creation of wxDbTable/wxDb objects
Moved code out of class constructors to a private function called from within the constructor
Moved destructor code to a cleanup() function so it could be called from within the constructor if the constructor failed.
Added wxDb::ModifyColumn() function.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@9255 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775