More <stdarg.h> cleanup; some are real bugs, some are just "don't do

More <stdarg.h> cleanup; some are real bugs, some are just "don't do
va_start and va_end unless you're actually going to use the va_list"
(those bring the va_start and va_end closer to the use point, which
makes it a little more obvious that we're using <stdarg.h> correctly and
makes it a little harder to use it incorrectly).

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@32963 f5534014-38df-0310-8fa8-9805f1628bb7