Using directory-grouping in host.xml servers element fails

Attempting to start a server when <servers directory-grouping="by-type"> is set fails.

[Host Controller] 10:30:20,760 ERROR [org.jboss.as.host.controller] (Controller Boot Thread) JBAS010907: Failed to start server (server-two): java.lang.IllegalArgumentException: No enum const class org.jboss.as.host.controller.DirectoryGrouping.by-type
[Host Controller] at java.lang.Enum.valueOf(Enum.java:196) [classes.jar:1.6.0_31]
[Host Controller] at org.jboss.as.host.controller.DirectoryGrouping.valueOf(DirectoryGrouping.java:33) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.DirectoryGrouping.fromModel(DirectoryGrouping.java:80) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.ModelCombiner.getServerLaunchCommand(ModelCombiner.java:262) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.ModelCombiner.createConfiguration(ModelCombiner.java:178) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.ServerInventoryImpl.createManagedServer(ServerInventoryImpl.java:476) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.ServerInventoryImpl.startServer(ServerInventoryImpl.java:163) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.ServerInventoryImpl.startServer(ServerInventoryImpl.java:150) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.DomainModelControllerService$DelegatingServerInventory.startServer(DomainModelControllerService.java:521) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.operations.StartServersHandler.cleanStartServers(StartServersHandler.java:114) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.operations.StartServersHandler.access$300(StartServersHandler.java:50) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.operations.StartServersHandler$1.execute(StartServersHandler.java:94) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:385) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.AbstractOperationContext.doCompleteStep(AbstractOperationContext.java:272) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.AbstractOperationContext.completeStep(AbstractOperationContext.java:200) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.domain.controller.operations.coordination.PrepareStepHandler.executeDirect(PrepareStepHandler.java:122) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.domain.controller.operations.coordination.PrepareStepHandler.execute(PrepareStepHandler.java:74) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.AbstractOperationContext.executeStep(AbstractOperationContext.java:385) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.AbstractOperationContext.doCompleteStep(AbstractOperationContext.java:272) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.AbstractOperationContext.completeStep(AbstractOperationContext.java:200) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.ModelControllerImpl.execute(ModelControllerImpl.java:121) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.DomainModelControllerService.startServers(DomainModelControllerService.java:443) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.host.controller.DomainModelControllerService.boot(DomainModelControllerService.java:403) [jboss-as-host-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at org.jboss.as.controller.AbstractControllerService$1.run(AbstractControllerService.java:155) [jboss-as-controller-7.1.1.Final.jar:7.1.1.Final]
[Host Controller] at java.lang.Thread.run(Thread.java:680) [classes.jar:1.6.0_31]

The cause is DirectoryGrouping.fromModel() is using an insufficiently sophisticated approach that would only work with the values BY_TYPE or BY_SERVER. Those values are not what will get stored in the model.