Clean up buff.c changes in NT port. Replace fb->is_socket with B_SOCKET

flag.  include http_main.h.  Create buff_write() and buff_read() static
functions in buff.c to increase readability/maintainability.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@78320 13f79535-47bb-0310-9956-ffa450edef68