minor changes to table/column comment code

minor changes to table/column comment code

Updates Changes.

Mentions Oracle support in generate_pod POD in ::Loader::Base.

Adds checking for generic comments via ->next::method in ::DBI::Oracle
as well.

Wraps table/column comment queries for MySQL on information_schema in
try blocks, as not all versions of MySQL have information_schema (5.0+
 do.)

Changes MySQL comment tests to use the new slurp_file util.

Makes the test messages in t/30_*.t more clear.