[libc] Add isprint()

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[test] Add okx() macro taking an explicit file name and line number

Allow test reports to specify an explicit file name and line number
using the extended okx() macro.  This allows large blocks of test
report code such as tcpip_random_ok() to be implemented as functions
rather than macros.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[deflate] Add support for DEFLATE decompression

Signed-off-by: Michael Brown <mcb30@ipxe.org>