Change connection and results charsets to utf8mb4 on MySQL 5.5.3+

[mfb]

CiviCRM isn't using utf8mb4 yet, but let's start the process of migrating to utf8mb4... We can use utf8mb4 as the connection and results charset on MySQL 5.5.3+

[civibot]

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[colemanw]

@mlutfy can you review?

[mfb]

@totten this PR is essentially the same as civicrm/civicrm-setup#16 so I think it could be a candidate for being merged (the version logic is in the query itself rather than in PHP code).

[totten]

@mfb yup, agree that looks sensible.

[totten]

jenkins, test this please

[totten]

It's also good to get this in at the start of the dev-cycle, which would be now. :)

Adding merge-on-pass. Small proviso: after the test-suite passes, but before merging, just do a quick login on the autobuild test site.