Add some additional routine variants that handle string encodings, and

Add some additional routine variants that handle string encodings, and
make FT_STRING and FT_UINT_STRING handle string encodings.

Get rid of FT_EBCDIC in favor of FT_STRING with ENC_EBCDIC.

Add some URLs for DRDA.

Clean up some stuff in TN3270 and TN5250, including using ENC_ values
for proto_tree_add_item().

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@37909 f5534014-38df-0310-8fa8-9805f1628bb7