Clean up configure check for libsmi.

First, check for smi.h.  If we don't have it, don't check for anything
else.

If we do have it, check for libsmi containing smiInit.  If we don't have
it, don't check for anything else.

If we do have it, check, with our test program, whether we can use it.

If that succeeds, prepend -lsmi to LIBS, and set USE_LIBSMI.  Otherwise,
don't do either of those.

Check, in source, *only* for USE_LIBSMI.  If it's set, use libsmi,
otherwise don't - don't even include smi.h, even if we happened to have
found it, and don't print the libsmi version string.
comma in AC_MSG_ERROR confuses configure
these changes to aclocal let tcpdump, when build out of source tree,
to find a libpcap that is adjacent to it, also built out of source tree
tcpdump 4.6.2 release
Mark the most recent items as changes for 4.6.2.
Document --with-sandbox-capsicum.
Update version now that 4.6.2 has been released.
Fix PPI header and payload printing.

Header printing (-e) had a stray ", " before the header; remove it.

Payload printing was skipping only the fixed portion of the PPI header,
not the entire header.
Add PPI printing fixes.