Fixes#755
Also consolidates WriteTokenInternal into matching WriteToken (slightly reduce
assembly size).
Also extend ExceptionAssert.Throws to return exception for further examination.
GetValueOrDefault() is an easily-inlined access to a field as this
will hold the correct value for both HasValue and !HasValue cases.
The Value property in comparison contains a branch on a check that the
Nullable<T> has its internal hasValue flag to decide whether to throw
InvalidOperationException or not.
Hence when a nullable type is known to have a value (not be null) and
one wants the value, rather than to possibly trigger the exception-throw
GetValueOrDefault() has a slight performance benefit over Value.
Accordingly, replace calls to the Value property with calls to
GetValueOrDefault() when previous checks or assignments guarantee the
value is not null.
Jon Hanna