Don't use capital letters in protocol abbreviation names - that obliges

Don't use capital letters in protocol abbreviation names - that obliges
people to type capital letters in filter expressions, which is a bit
rude.  Furthermore, we're not using "Hilscher" in field names, we're
using "hilscher".  This should fix bug 2310 - we check for various
illegal characters in filter names, including capital letters, and crash
if they're found.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@24496 f5534014-38df-0310-8fa8-9805f1628bb7