metamail format string bugs and buffer overflows

Ulf Härnhammar reported four bugs in metamail: two are format
string bugs and two are buffer overflows. The bugs are in
SaveSquirrelFile(), PrintHeader(), and ShareThisHeader().
These vulnerabilities could be triggered by a maliciously
formatted email message if metamail' or splitmail’ is used
to process it, possibly resulting in arbitrary code execution
with the privileges of the user reading mail.