Consolidate libbuffer sources into singe file.

Merged libbuffer.a sources into a single source file buffer.c. This
helps to sift through different function definitions while debugging
or tracing function call sequence etc. Removed the now empty source
files.

Changed Makefile.am to remove unnecessary sources from the dependency
list.
Remove compiler warnings - 01.

This patch is to fix complier warnings about unmatched argument
types using type casting.
Remove compiler warnings - 02.

Changed cdb.c and common.c to fix compiler warnings about signed
unsigned integer comparison.
Remove compiler warnings - 03.

Minor changes to dns_rcip.c, dns_rcrw.c & dns_transmit.c to fix
compiler warnings about signed unsigned integer comparison.