ar.c now uses a linked list to process headers, uses getopt, new internal function...

ar.c now uses a linked list to process headers, uses getopt, new internal function extractAr(srcFD, dstFd, filename) to make it easily accessable to other busybox functions.

moved copySubFile from ar.c to utilities.c

modified dd.c to use fullWrite

modified copyFile in utilities.c to use copySubFile