* _scm.h: Removed #include <errno.h>.

* _scm.h: Removed #include <errno.h>.

* error.c, net_db.c, putenv.c, stime.c: Removed declaration of
errno variable (can be a macro on some systems, for example when
using linux libc with threads).

* error.c, filesys.c, gc.c, ioext.c, iselect.c, net_db.c, ports.c,
posix.c, print.c, putenv.c, scmsigs.c, script.c, simpos.c, smob.c,
socket.c, srcprop.c, stime.c, strop.c, unif.c, vports.c: Added
#include <errno.h> in these 20 out of 100 files.