[BUGFIX] Ambiguous XCLASS naming tx_em_Connection_ExtDirectServer

The naming for XCLASSing tx_em_Connection_ExtDirectServer is written
with and without underscore between "connection" and "extdirectserver".

Change-Id: Ifcdc2c52643473eb48b4be2c91d72248e2340bdd
Resolves: #32596
Releases: 4.7, 4.6, 4.5
Reviewed-on: http://review.typo3.org/7330
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert