[patch] adds plugin_file and one function, readline

[cmaj]

A single line of text from a file can be read by the plugin by specifying the name of the file and the line number to read. Example:

Widget weatherline {
    class 'Text'
    expression file::readline('/tmp/weather',1)
    width 20
    align 'M'
    update 1000
}

[michael]

Commited to CVS. Thanks a lot for your contribution!