datadict: different results when column is modified between alterColumnSql() and changeTableSQL()

[mnewnham]

If the same simple change to the schema of a table is applied to a column using the above 2 methods, the output is completely different. This is because ''changeTableSql()'' does not call the database specific method, but instead uses the generic base method. So using the following change to a table:

'regiondescription C(100) NOTNULL DEFAULT "BILL"';

When passed to ''alterColumnSql()'', the result is

Array
(
    [0] => ALTER TABLE region ALTER COLUMN regiondescription VARCHAR(100) NOT NULL
    [1] => ALTER TABLE region ADD CONSTRAINT DF__region__regiondescription__51a89880 DEFAULT 'BILL' FOR regiondescription
)

When passed to ''changeTableSql()''

Array
(
    [0] => ALTER TABLE region ALTER COLUMN regiondescription VARCHAR(100) DEFAULT 'BILL' NOT NULL
)

In addition, ''changeTableSql()'' now calls the driver specific ''dropColumnSql()'' instead of using the generic method in case of column drops.

This issue was previously reported by @boshrin on #383 For Postgres/xmlSchema but covers all drivers using the datadict feature, thx for the code snippet.