It looks like NV50+ hardware gets you infinities and NaN's in D3D as well for
most things, so we should only need special handling for pow and nrm.

The server won't actually send the event until the request is done.

This matches what WineEngCreateFontInstance() does, and makes applications
which set custom axes directions using different window/viewport extents
display text correctly.

As Eric Anholt pointed out, using length() here is suboptimal. It essentially
translates into "inversesqrt(dot(x, x));", but needs to handle the case of
zero-length vectors, much like nrm.

This is mostly for consistency, in practice ddraw code is never going to use
this format.