i965: Be more careful with the interleaved user array upload optimization

The checks to determine when the data can be uploaded in an interleaved
fashion can be tricked by certain data layouts.  For example,

    float data[...];

    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 16, &data[0]);
    glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 16, &data[4]);
    glDrawArrays(GL_POINTS, 0, 1);

will hit the interleaved path with an incorrect size (16 bytes instead
of 32 bytes).  As a result, the data for attribute 1 never gets
uploaded.  The single element draw case is the only sensible case I can
think of for non-interleaved-that-looks-like-interleaved data, but there
may be others as well.

To fix this, make sure that the end of the element in the array being
checked is within the stride "window."  Previously the code would check
that the begining of the element was within the window.

NOTE: This is a candidate for stable branches.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>

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