Changed MySQL Inserts to Insert Ignores

For MySQL, the "INSERT INTO" can be changed to "INSERT IGNORE INTO" so that the installation script can be used as a recovery script if core extensions are uninstalled via the admin. What the ignore will do is ignore entries that are already there and only insert when an entry doesn't exist. I'm not sure what the equivalents are in postgresql and sqlazure.

Documentation for Insert Ignore can be found at http://dev.mysql.com/doc/refman/5.5/en/insert.html

#### Steps to reproduce the issue:
Check https://github.com/joomla/joomla-cms/blob/master/installation/sql/mysql/joomla.sql


#### Expected result:
INSERT IGNORE INTO


#### Actual result:
INSERT INTO

#### Additional info:

[feedback from Michael]
Neither of the other databases have that type of support without some creative hacking.
[/feedback]