add platform abstraction for errno and strerror, check EWOULDBLOCK additionally to EAGAIN
add ability to use socketspair instead of pipe, implement W32 pipe/socketspair emulation

configure.ac: add "--disable-pipes" option
gmtime_r() replacement on W32, add error check in get_date_string()
test_get_sendfile.c - remove DIR_SEPARATOR_STR (W32 works fine with forwardslashes)
remove inet_pton() from tests, use real IPv6 loopback for test
add sleep() and usleep() replacement for W32
replace random() -> rand(), initialize with srand() for more random numbers
Remove PlibC wrappers and macros
Replace plibc_init() and plibc_shutdown()
Remove PlibC from platform.h
Remove PlibC from autotools files
Remove PlibC files