Fix creation of frames on MS-Windows: don't cons Lisp objects in input thread.

Fix creation of frames on MS-Windows: don't cons Lisp objects in input thread.

 src/w32fns.c (w32_createwindow): Accept an additional argument, an
 array of 2 values specifying the coordinates of the frame's
 top-left corner.  Use these values instead of calling x_get_arg,
 which can cons Lisp objects, and therefore cannot be called except
 from the main thread.  Remove redundant tests for the default
 values.
 (my_create_window): Move the calculation of the coordinates of the
 frame's top-left edge here.  Pass them to the input thread via the
 second parameter of the WM_EMACS_CREATEWINDOW message.  See
 http://lists.gnu.org/archive/html/emacs-devel/2014-09/msg00892.html
 for the details.