Patches for files in libpcap

Michael,

    These patches explicitly set pointer variables released by free() to NULL, and in optimize.c, improves the error message strings which are sent to bpf_error() when a request to malloc()/calloc() fails.  I also changed the expression test of (!offset) to (offset == NULL) in optimize.c to maintain consistency with other checks made after malloc()/calloc().

All files were explicitly set to :set fileformat=unix <enter> prior to leaving VIM in Git BASH.  Sorry for the problems earlier, now that I know that Git BASH allows me to edit without goofing up, additional patches should be much easier in the future...

Bill