由于ubuntu/debian软件库中有时候不同的库更新速度不一致，apt-get 出出现如下的错误提示

Some packages could not be installed. This may mean that you have

requested an impossible situation or if you are using the unstable

distribution that some required packages have not yet been created

or been moved out of Incoming.

The following information may help to resolve the situation:

The following packages have unmet dependencies:

libssl-dev: Depends: libssl0.9.8 (= 0.9.8k-7ubuntu8) but 0.9.8k-7ubuntu8.5 is to be installed

这个时候应该请令一个工具出马了："aptitude"
使用这个工具，当某个库依赖的库与当前版本不一致时，aptitude 会尝试降级当前这个库的版本，同时解决降级这个库对其它软件的依赖性的影响， 最终成功安装apt-get 没法安装的软件。

via.http://hi.baidu.com/firstchenjie/blog/item/afcdbc21eb25c2b04723e800.html