pthreads: more locking

lib/client/client-handshake.c

lib/context.c

lib/event-libs/libuv.c

lib/libwebsockets.c

lib/plat/lws-plat-unix.c

lib/pollfd.c

lib/private-libwebsockets.h

lib/server/cgi.c

lib/server/parsers.c

lib/server/server.c

lib/server/ssl-server.c

lib/service.c

test-apps/test-server-pthreads.c