Fix format of ALTER TABLE statements for Oracle
Fix backcompat detection on Oracle, where NULL != 'string' is false

The 4.1.13 backcomapt file is meant to run for all earlier upgrade steps
where the code assumes that limits on groups can be done on Name.
Before it runs, it checks if there are SystemInternal rows where the
Name is different from the Type, to ensure it does not run more than is
necessary.

Unfortunately, this does not work on Oracle, where Name is NULL on
SystemInternal groups -- and Oracle's treatment of NULL means that the
rows thus do not match, and thus the back-compat step does not run.
Because of this, the upgrade process runs into trouble, for instance in
the 4.1.4 upgrade step:

    [error]: Can't load role group AdminCc: Couldn't find row
    [error]: Can't load role group Cc: Couldn't find row
    [error]: Can't load role group Owner: Couldn't find row
    [error]: Can't load role group Requestor: Couldn't find row

Resolve this by alternately checking if the Name of the SystemInternal
groups IS NULL; this is also still a correct alternate condition to
check on other, non-Oracle, databases.
Indexes, like schema, needs to set the CURRENT_SCHEMA on oracle

Otherwise, attempts to create indexes result in "table or view does not
exist" because the tables are not in the current schema.  Additionally,
the created indexes would be in the wrong schema.
Switch to _arrayref so that case of returned columns is irrelevant

Despite being asked for the 'uniqueness' colun, Oracle may return
'UNIQUENESS' in the hashref.  Use array references instead, to step
around this inconsistency -- as is already done for all other database
types.
Dropping an Oracle index may instead require dropping a constraint

A couple columns in RT contain contraints, not just unique indexes.
Attempting to drop such indexes results in the error "cannot drop index
used for enforcement of unique/primary key".

Look for the constraints in the DBA_CONSTRAINTS table, and make use of
ALTER TABLE ... DROP CONSTRAINT to remove them, rather than DROP INDEX.
There may be more than one index that begins the way we are looking for

Specifically, on Oracle, 4.0 contains both Queues_Name_Unique and
Queues1, as well as Users_Name_Unique and Users2.
Adjust log levels for consistency with 5d75726
Merge branch '4.2/oracle-upgrade' into 4.2-trunk