Give _defaultOf() precedence over default constructor calls

This is a post-release cleanup that resolves the competition between _defaultOf() and user default constructor calls.

When the _defaultOf() feature was added, it provided type-specific default values for all types but did not call a user-defined default constructor if it was available.  (Instead, it called the compiler-supplied all-fields constructor -- behavior that was consistent with the existing implementation at that time.)  When I added user-default constructor calls, I did so in a way that would prefer the user-default constructor if it was present and otherwise use defaultOf().

That's not a particularly good design, because whether _defaultOf() is called for a particular type depends on whether a user-defined default constructor is present for that type.  If the user was also overriding _defaultOf(), he would have to read the spec to discover why his routine was not being called.  It is more consistent to give either _defaultOf() or the default constructor absolute priority.  If priority were given to default constructor calls, then the need for _defaultOf() would vanish.  But doing that depends on being able to initialize a variable of fundamental type by calling a constructor on it.  This is currently unsupported.

That makes _defaultOf() the obvious choice.  It provides a shim to support default initialization for types that do not yet expose constructors, and with this change, its default behavior for records is consistent with calling the zero-args constructor directly.

###THE CHANGE
In the place where resolution used to call the user-default constructor if it existed and _defaultOf() otherwise, _defaultOf() is now called unconditionally.  In the place where the compiler-supplied implementation of _defaultOf() for records used to call the compiler-generated all-fields constructor, it now calls the zero-args constructor by name.  Removing the special case for user-defined default constructor calls from resolution allowed a considerable amount of redundant code to be removed.
Would you mind updating the comment here?  (I know it is my comment, sorry for the lack of clarity in it) "The function" should be replaced with "This defaultOf function".