Don't link plugins against libwireshark: any program that loads the dissector

Don't link plugins against libwireshark: any program that loads the dissector
plugins should already be linked against libwireshark.

Don't link capinfos and editcap against libwireshark: they only needed to be
because the plugins were linked against libwireshark (see rev 24123 and the
ensuing discussion on -dev).

capinfos and editcap: don't complain if plugins fail to load: dissector
plugins should fail to load because they need libwireshark.  I am assuming
here that wiretap plugins don't need libwireshark (I've never seen such a
plugin but LEGO's code and comments suggest this is the case).

(The goal of this checkin is to stop linking capinfos and editcap against
libwireshark while still allowing wiretap plugins.  Since we don't have any
such plugins in the tree I do somewhat doubt the need for all this but I don't
want to be the one to remove the functionality.)

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@24650 f5534014-38df-0310-8fa8-9805f1628bb7