usleep is deprecated and disabled in glibc 2.12 unless requested. Use
nanosleep instead if available.
This fixes the following compiler warning:
./src/zrtp_iface_scheduler.c: In function 'zrtp_sleep':
./src/zrtp_iface_scheduler.c:96:2: warning: implicit declaration of
function 'usleep' [-Wimplicit-function-declaration]
usleep(msec*1000);
^
Thanks to Phil Zimmermann for the code and for the license exception
we needed to include it.
There remains some build system integration work to be done before
this code will build properly in the FreeSWITCH tree.
