Use Clap's non-exiting functions

The better to test with.

src/cli/errors.rs

@@ -20,6 +20,7 @@ error_chain! {
     }
 
     foreign_links {
+        Clap(clap::Error);
         Temp(temp::Error);
         Io(io::Error);
         Term(term::Error);

src/cli/rustup_mode.rs

@@ -55,7 +55,16 @@ where
 pub fn main() -> Result<utils::ExitCode> {
     self_update::cleanup_self_updater()?;
 
-    let matches = cli().get_matches_from(process().args_os());
+    let matches = match cli().get_matches_from_safe(process().args_os()) {
+        Ok(matches) => Ok(matches),
+        Err(e)
+            if e.kind == clap::ErrorKind::HelpDisplayed
+                || e.kind == clap::ErrorKind::VersionDisplayed =>
+        {
+            return Ok(utils::ExitCode(0))
+        }
+        Err(e) => Err(e),
+    }?;
     let verbose = matches.is_present("verbose");
     let quiet = matches.is_present("quiet");
     let cfg = &mut common::set_globals(verbose, quiet)?;

src/cli/setup_mode.rs

@@ -87,7 +87,16 @@ pub fn main() -> Result<utils::ExitCode> {
                 .help("Don't configure the PATH environment variable"),
         );
 
-    let matches = cli.get_matches_from(process().args_os());
+    let matches = match cli.get_matches_from_safe(process().args_os()) {
+        Ok(matches) => matches,
+        Err(e)
+            if e.kind == clap::ErrorKind::HelpDisplayed
+                || e.kind == clap::ErrorKind::VersionDisplayed =>
+        {
+            return Ok(utils::ExitCode(0))
+        }
+        Err(e) => Err(e)?,
+    };
     let no_prompt = matches.is_present("no-prompt");
     let verbose = matches.is_present("verbose");
     let quiet = matches.is_present("quiet");

tests/mock/clitools.rs

@@ -493,13 +493,16 @@ where
     //   collected for assertions to be made on it as our tests traverse layers.
     // - self update executions cannot run in-process because on windows the
     //    process replacement dance would replace the test process.
+    // - any command with --version in it is testing to see something was
+    //   installed properly, so we have to shell out to it to be sure
     if name != "rustup" {
         return false;
     }
     let mut is_update = false;
     let mut no_self_update = false;
     let mut self_cmd = false;
     let mut run = false;
+    let mut version = false;
     for arg in args {
         if arg.as_ref() == "update" {
             is_update = true;
@@ -509,9 +512,11 @@ where
             self_cmd = true;
         } else if arg.as_ref() == "run" {
             run = true;
+        } else if arg.as_ref() == "--version" {
+            version = true;
         }
     }
-    !(run || self_cmd || (is_update && !no_self_update))
+    !(run || self_cmd || version || (is_update && !no_self_update))
 }
 
 pub fn run<I, A>(config: &Config, name: &str, args: I, env: &[(&str, &str)]) -> SanitizedOutput