http://www.autoitscript.com/forum/topic/64867-screencapture-doesnt-support
-multiple-monitors/?p=787718
缩：http://ppt.cc/e6pv
做纪录用，在双萤幕环境试过可行，无三萤幕可测，可做全画面撷图。
;SM_CXVIRTUALSCREEN = 78
$iVScrWidth=_WinAPI_GetSystemMetrics(78)
;SM_CYVIRTUALSCREEN = 79
$iVScrHeight=_WinAPI_GetSystemMetrics(79)