Fix doctests that used ignore to hide code that didn't compile.

src/cargo/core/features.rs

@@ -21,7 +21,7 @@
 //! 3. To actually perform the feature gate, you'll want to have code that looks
 //!    like:
 //!
-//! ```rust,ignore
+//! ```rust,compile_fail
 //! use core::{Feature, Features};
 //!
 //! let feature = Feature::launch_into_space();

src/cargo/util/network.rs

@@ -73,9 +73,12 @@ fn maybe_spurious(err: &Error) -> bool {
 ///
 /// # Examples
 ///
-/// ```ignore
-/// use util::network;
-/// cargo_result = network::with_retry(&config, || something.download());
+/// ```
+/// # use crate::cargo::util::{CargoResult, Config};
+/// # let download_something = || return Ok(());
+/// # let config = Config::default().unwrap();
+/// use cargo::util::network;
+/// let cargo_result = network::with_retry(&config, || download_something());
 /// ```
 pub fn with_retry<T, F>(config: &Config, mut callback: F) -> CargoResult<T>
 where