Do startup things in an order more like that of gtkshark.

Get credential information and drop privileges *very* early on.  Get the
pathname of the executable right after that, then initialize the 802.11
decryption, then, on Windows, load WinPcap and, if available, AirPcap.
*Then* we can get the version information and set the crash information.

We should drop privileges as early as possible.

We have to load WinPcap and AirPcap before getting the run-time
information, as the run-time information includes the *pcap versions.

Change-Id: Ib40e5a848cc7f42fcb424faa15a91868eaa0b9a4
Reviewed-on: https://code.wireshark.org/review/2733
Reviewed-by: Guy Harris <guy@alum.mit.edu>