Decode headers in multipart messages sub-bodies.

This is useful for, eg, when attachement filenames are not in ASCII encoding
Eunit test for decode-multipart-headers patch #36
Fix for typo in previous patches. Small change in test case to prevent Erlang character set issues.
Merge branch 'master' of git://github.com/Vagabond/gen_smtp

Conflicts:
	src/mimemail.erl