Add a module to wiretap to be able to read trace files from Toshiba's

Add a module to wiretap to be able to read trace files from Toshiba's
line of ISDN routers. Much like the ascend reader, this module reads an
ASCII hex dump of trace data.

Rearranged the order in which wiretap tries trace files, to keep the
ASCII-readers (ascend and toshiba) at the end, and put the binary-readers
(everything else) at the front of the list. If a telnet session of
and ascend trace or toshiba trace were captured near the beginning of
another trace, wiretap might think the trace was ascend or toshiba if it
tried that module first.

Fixed the way wtap_seek_read() selects functions to call. It was using
the encap type instead of the file type. We got lucky because
WTAP_ENCAP_ASCEND == WTAP_FILE_ASCEND

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@952 f5534014-38df-0310-8fa8-9805f1628bb7