CFLAGS and LDFLAGS, and remove lib prefix.  [ruby-dev:20993]

* file.c (rb_file_s_rename): retry with removing new file on
  DOSISH.  [ruby-dev:21007]

* ext/socket/extconf.rb (sendmsg, recvmsg): check functions.

* ext/socket/socket.c (unix_send_io, unix_recv_io): raise
  NotImplementedError unless system calls are available.

* ext/socket/socket.c (sock_initialize): rename from sock_init()
  to get rid of conflict with OS/2 socket library.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@4221 b2dd03c8-39d4-4d8f-98ff-823fe69b080e