Applied patch [ 649284 ] Fix wxODBC to work with MySQL 2.x

Applied patch [ 649284 ] Fix wxODBC to work with MySQL 2.x

The current sample/db fails to build indexes with
MyODBC v2.50.39

This is due to two problems:

(1) wxDb::ModifyColumn() created a SQL statement that
was not correctly formed for MySQL. This problem
caused wxDbTable::CreateIndex() to fail to set the
columns that are going to indexes to be NOT NULL. I
fixed this by added a special case for MySQL.

(2) When creating an Index on a VARCHAR column,
MySQL requires a key length to be specified.
wxDbTable::CreateIndex() current does not do this. I
fixed this problem by adding code to do this.

The attached patch file patches dbtable.cpp and db.cpp
on the 2.5 branch.

gor Mikolic-Torreira

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@18145 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775