Fix invalid usage of MSBuild task parameters

[sliekens]

This commit does two things:

• converts Roundhouse.RecoveryMode to an explicit implementation of ConfigurationPropertyHolder.RecoveryMode
• adds a property with the same name of type System.String

Both properties get and set the same private field.

Fixes #131

[ferventcoder]

Pretty sure this won't affect Nant adversely as the condition is now a string. Should be pretty transparent (not that anyone is actually using the Nant task haha).

[ferventcoder]

Thanks!

[sliekens]

Oops. I just remembered that throwing an exception is not the best way to raise MSBuild errors.

DBDeploy_MSBuild.proj(21,5): error MSB4018: The "Roundhouse" task failed unexpectedly.\r
DBDeploy_MSBuild.proj(21,5): error MSB4018: System.ArgumentOutOfRangeException: The value of 'RecoveryMode' must be one of these values: 'NoChange', 'Simple' or 'Full'.\r
DBDeploy_MSBuild.proj(21,5): error MSB4018: Parameter name: value\r
DBDeploy_MSBuild.proj(21,5): error MSB4018: Actual value was NoChanges.\r
DBDeploy_MSBuild.proj(21,5): error MSB4018:    at roundhouse.tasks.Roundhouse.set_RecoveryMode(String value)
DBDeploy_MSBuild.proj(56,17): error MSB4026: The "RecoveryMode=NoChanges" parameter for the "Roundhouse" task is invalid.
DBDeploy_MSBuild.proj(21,5): error MSB4063: The "Roundhouse" task could not be initialized with its input parameters.

[ferventcoder]

open another PR and reference this.