[Glamor] [PATCH] Add the poly line draw feature for glamor.

[Zhigang Gong]

I have two comments on this patch.

1. For comparison two floats/int with ">" or "<" ops, you don't need to add a
epsilon which is only needed when you want to check whether the two floats are
equal to each other. And I simply some of you code remove some uncessary 
type cast.

2. One time draw one line segment is not efficient, you can accumulate all the lines and
draw them all at one call toe glDrawArray.

I fixed the comment 1 and paste the new version as below. please check it out.
For 2, I discussed with you, and please refine them latter. Anyway, 
this patch is already much better than original fully fallback to CPU when
draw diagonal poly_line.

But just before I pushed this patch, I found regressions with XTS test.
xts5/Xlib9/XDrawLines/XDrawLines (32/104): FAIL
xts5/Xlib9/XDrawLines/XDrawLines (57/104): FAIL

There are also two or three failures on XDrawLine, please check and fix
the regressions. Thanks.