Unsurprisingly, since <unistd.h> was so darn hard to find for OpenSSL developers

Unsurprisingly, since <unistd.h> was so darn hard to find for OpenSSL developers
they had resorted to manually protyping read(2) instead of incredible amount of
preprocessor wizardry needed to find the ever illusive <unistd.h>. Let's just
include <unistd.h> and we don't need to do this.. While we're at it flense
out _OSD_POSIX and __DGJPP__ cruft.
ok krw@