Discard torrent file if path data in it contains directory
traversal directives. Discard metalink:file element in Metalink3
format if its name attribute contains directory traversal
directives. Ignore name attribute of metalink:signature element
in Metalink3 format if it contains directory traversal directives.
* src/MetalinkParserStateV3Impl.cc
* src/bittorrent_helper.cc
* src/message.h
* test/BittorrentHelperTest.cc
* test/Makefile.am
* test/MetalinkProcessorTest.cc
* test/metalink3-dirtraversal.xml
* test/test.xml
