Release pcap-thread 4.2.0

Added two new functions, pcap_thread_open_offline_fp() to open a PCAP based on a FILE* and pcap_thread_ftell() to get the byte position in the input.

Changed pcap_thread_run() to run a separate loop when all input are offline PCAPs.

Improved error messages by adding an internal function, pcap_thread_handle_pcap_error(), to handle all PCAP errors and use pcap_geterr() or pcap_statustostr() to get details depending on the error.

Update autotools requirement to v2.69 and updated AX macros.

a55a1bc Error handling, open offline
92b2165 sys/time.h
42e5bf2 autotools, fopen, ftell