Rename WTAP_ERR_BAD_RECORD to WTAP_ERR_BAD_FILE; it really reports any

Rename WTAP_ERR_BAD_RECORD to WTAP_ERR_BAD_FILE; it really reports any
form of corruption/bogosity in a file, including in a file header as
well as in records in the file.  Change the error message
wtap_strerror() returns for it to reflect that.

Use it for some file header problems for which it wasn't already being
used - WTAP_ERR_UNSUPPORTED shouldn't be used for that, it should only
be used for files that we have no reason to believe are invalid but that
have a version number we don't know about or some other
non-link-layer-encapsulation-type value we don't know about.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@40175 f5534014-38df-0310-8fa8-9805f1628bb7