Improvements to unredirect windows

Substantial improvement on fullscreen performance, not as much with windowed - though I'm only using glxgears, there may be other advantages I haven't witnessed.

1.8.1
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[~]$ glxgears
19947 frames in 5.0 seconds = 3989.379 FPS
22190 frames in 5.0 seconds = 4437.846 FPS
21510 frames in 5.0 seconds = 4301.961 FPS
22896 frames in 5.0 seconds = 4579.125 FPS
21534 frames in 5.0 seconds = 4306.488 FPS
22767 frames in 5.0 seconds = 4553.094 FPS
22742 frames in 5.0 seconds = 4548.019 FPS
21104 frames in 5.0 seconds = 4220.704 FPS
21722 frames in 5.0 seconds = 4344.329 FPS
19216 frames in 5.0 seconds = 3843.100 FPS
16764 frames in 5.0 seconds = 3352.772 FPS
23092 frames in 5.0 seconds = 4618.221 FPS
22154 frames in 5.0 seconds = 4430.722 FPS
^C
[~]$ glxgears -fullscreen
1984 frames in 5.0 seconds = 396.792 FPS
1873 frames in 5.0 seconds = 374.473 FPS
1846 frames in 5.0 seconds = 368.980 FPS
1840 frames in 5.0 seconds = 367.926 FPS
1859 frames in 5.0 seconds = 371.795 FPS
1904 frames in 5.0 seconds = 380.732 FPS
1892 frames in 5.0 seconds = 378.265 FPS
1877 frames in 5.0 seconds = 375.255 FPS
1886 frames in 5.0 seconds = 377.070 FPS
1870 frames in 5.0 seconds = 373.930 FPS
1877 frames in 5.0 seconds = 375.246 FPS
1856 frames in 5.0 seconds = 371.059 FPS
1849 frames in 5.0 seconds = 369.741 FPS

With these commits
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[~/bin]$ glxgears
21924 frames in 5.0 seconds = 4384.526 FPS
23216 frames in 5.0 seconds = 4640.062 FPS
22640 frames in 5.0 seconds = 4527.917 FPS
23624 frames in 5.0 seconds = 4724.617 FPS
21631 frames in 5.0 seconds = 4326.158 FPS
23034 frames in 5.0 seconds = 4606.602 FPS
22584 frames in 5.0 seconds = 4516.769 FPS
22004 frames in 5.0 seconds = 4400.701 FPS
23379 frames in 5.0 seconds = 4675.474 FPS
19138 frames in 5.0 seconds = 3827.507 FPS
22735 frames in 5.0 seconds = 4546.911 FPS
21897 frames in 5.0 seconds = 4379.214 FPS
16753 frames in 5.0 seconds = 3350.455 FPS
^C
[~/bin]$ glxgears -fullscreen
5898 frames in 5.0 seconds = 1179.488 FPS
6736 frames in 5.0 seconds = 1347.172 FPS
6730 frames in 5.0 seconds = 1345.839 FPS
6738 frames in 5.0 seconds = 1347.517 FPS
6733 frames in 5.0 seconds = 1346.588 FPS
6732 frames in 5.0 seconds = 1346.267 FPS
6735 frames in 5.0 seconds = 1346.995 FPS
5862 frames in 5.0 seconds = 1172.253 FPS
6730 frames in 5.0 seconds = 1345.852 FPS
6737 frames in 5.0 seconds = 1347.281 FPS
6735 frames in 5.0 seconds = 1346.902 FPS
6736 frames in 5.0 seconds = 1347.034 FPS
6733 frames in 5.0 seconds = 1346.459 FPS
6737 frames in 5.0 seconds = 1347.235 FPS