show changes for a certain revision in svn

In order to show the source code changes for a certain revision "RVSN", use the following command:
> svn diff -c RVSN

hide tab in Thunderbird

In order to hide the tab in Thunderbird and increase the useful window area, set the option "mail.tabs.autoHide" to "true" by using the Config Editor (accessible from Preferences > Advanced > General). If more that one tab are created, then the area is displayed again.

map Alt key in Linux when logging from Mac OS X

When logging from Mac OS X in Linux via ssh, the Alt key seems not to be mapped correctly, and it cannot be used in emacs. The solution seems to be to run this command on the Mac OS X machine from which you connect:
xmodmap -e "keycode 66 = Meta_L"