相关疑难解决方法(0)

我刚刚为 GIMP 的开发版本添加了一个 PPA 存储库，但出现此错误：

$ apt-get update && apt-get upgrade
...
The following packages have been kept back:
  gimp gimp-data libgegl-0.0-0 libgimp2.0

为什么以及如何解决它以便我可以使用最新版本而不是我现在拥有的版本？

有时，当我安装东西时，我会收到如下错误：

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:
 package1 : Depends: package2 (>= 1.8) but 1.7.5-1ubuntu1 is to be installed
E: Unable to correct problems, you have held broken packages.

我该如何解决这个问题？