建议保存图片使用"过去最常用的文件夹"

[GoogleCodeExporter]

Win7特性允许在程序不指定保存文件夹的情况下, 
使用用户最常用的文件夹 :

"If lpstrInitialDir has the same value as was passed the first time the 
application used an Open or Save As dialog box, the path most recently selected 
by the user is used as the initial directory."
http://msdn.microsoft.com/en-us/library/windows/desktop/ms646839(v=vs.85).aspx

这样做是很方便的, 
毕竟不是每个人都喜欢把图片保存到"我的图片"
建议在SaveImage处做以下改动:
1. Use a GetVersionEx to determine the current OS
2. if win7, use a lpstrtInitialDir = ""; instead. As I tried, this may help 
that new behaviour work.

Original issue reported on code.google.com by fjy...@gmail.com on 27 May 2012 at 12:47