#4 Export results of multiple sessions

[mabecker]

I wanted to view the results of multiple tests I
performed via Ant in one single XML-file. But every new
session result made earlier results getting overwritten.
With this patch all results are successfully written into
one file if you run the tests via Ant or if you export a
result from the playback results view in eclipse.
Besides, the html-expressions for german umlauts such
as ä are translated to real umlauts before writing
the xml to the file und the file is encoded with ISO-8859-
15 (If you like an other encoding, change it). Thus really
silly error messages are prevented.

[mabecker]