E: Unable to correct problems, you have held broken packages.

在安装RVM来管理ruby时遇到一些库的版本问题

The following packages have unmet dependencies:
libreadline6-dev : Depends: libreadline6 (= 6.2-8) but 6.2-9 is to be installed

解决：

aptitude install libreadline6-dev

The following NEW packages will be installed:
libreadline6-dev{b}
0 packages upgraded, 1 newly installed, 0 to remove and 137 not upgraded.
Need to get 264 kB of archives. After unpacking 802 kB will be used.
The following packages have unmet dependencies:
libreadline6-dev : Depends: libreadline6 (= 6.2-8) but 6.2-9 is installed.
The following actions will resolve these dependencies:

Keep the following packages at their current version:
1) libreadline6-dev [Not Installed]

Accept this solution? [Y/n/q/?] n
The following actions will resolve these dependencies:

Downgrade the following packages:
1) libreadline6 [6.2-9 (now) -> 6.2-8 (precise)]

Accept this solution? [Y/n/q/?] y
The following packages will be DOWNGRADED:
libreadline6
The following NEW packages will be installed:
libreadline6-dev