Fix test_ptymaster_drop after PR #1098

This test cannot be compiled under Redox.  PR #1098 attempted to disable
it for Redox, but actually disabled it everywhere.  AFAICT, Cargo has no
syntax to conditionally enable a target, except based on features.
Instead, use conditional compilation within the test.

Cargo.toml

@@ -58,6 +58,6 @@ name = "test-mount"
 path = "test/test_mount.rs"
 harness = false
 
-[[target.'cfg(not(target_os = "redox"))'.test]]
+[[test]]
 name = "test-ptymaster-drop"
 path = "test/test_ptymaster_drop.rs"

test/test_ptymaster_drop.rs

@@ -1,19 +1,24 @@
-use nix::fcntl::OFlag;
-use nix::pty::*;
-use nix::unistd::close;
-use std::os::unix::io::AsRawFd;
+#[cfg(not(target_os = "redox"))]
+mod t {
+    use nix::fcntl::OFlag;
+    use nix::pty::*;
+    use nix::unistd::close;
+    use std::os::unix::io::AsRawFd;
 
-/// Regression test for Issue #659
-/// `PtyMaster` should panic rather than double close the file descriptor
-/// This must run in its own test process because it deliberately creates a race
-/// condition.
-#[test]
-#[should_panic(expected = "Closing an invalid file descriptor!")]
-// In Travis on i686-unknown-linux-musl, this test gets SIGABRT.  I don't know
-// why.  It doesn't happen on any other target, and it doesn't happen on my PC.
-#[cfg_attr(all(target_env = "musl", target_arch = "x86"), ignore)]
-fn test_double_close() {
-    let m = posix_openpt(OFlag::O_RDWR).unwrap();
-    close(m.as_raw_fd()).unwrap();
-    drop(m);            // should panic here
+    /// Regression test for Issue #659
+    ///
+    /// `PtyMaster` should panic rather than double close the file descriptor
+    /// This must run in its own test process because it deliberately creates a
+    /// race condition.
+    #[test]
+    #[should_panic(expected = "Closing an invalid file descriptor!")]
+    // In Travis on i686-unknown-linux-musl, this test gets SIGABRT.  I don't
+    // know why.  It doesn't happen on any other target, and it doesn't happen
+    // on my PC.
+    #[cfg_attr(all(target_env = "musl", target_arch = "x86"), ignore)]
+    fn test_double_close() {
+        let m = posix_openpt(OFlag::O_RDWR).unwrap();
+        close(m.as_raw_fd()).unwrap();
+        drop(m);            // should panic here
+    }
 }