update backtrace formating text tips

src/librustc_driver/lib.rs

@@ -1114,11 +1114,11 @@ pub fn monitor<F: FnOnce() + Send + 'static>(f: F) {
                              errors::Level::Note);
             }
             if match env::var_os("RUST_BACKTRACE") {
-                Some(val) => &val != "0",
+                Some(val) => (&val != "0") && (&val != "no"),
                 None => false,
             } {
                 handler.emit(&MultiSpan::new(),
-                             "run with `RUST_BACKTRACE=1` for a backtrace",
+                             "run with `RUST_BACKTRACE=yes` for a backtrace",
                              errors::Level::Note);
             }
 

src/libstd/panicking.rs

@@ -354,7 +354,7 @@ fn default_hook(info: &PanicInfo) {
             if let Some(format) = log_backtrace {
                 let _ = backtrace::print(err, format);
             } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
-                let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
+                let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=yes` for a backtrace.");
             }
         }
     };

src/libstd/sys_common/backtrace.rs

@@ -158,7 +158,7 @@ pub fn log_enabled() -> Option<PrintFormat> {
     }
 
     let val = match env::var_os("RUST_BACKTRACE") {
-        Some(x) => if &x == "0" {
+        Some(x) => if &x == "0" || &x == "no" {
             None
         } else if &x == "full" {
             Some(PrintFormat::Full)

src/test/run-pass/multi-panic.rs

@@ -16,7 +16,7 @@ fn check_for_no_backtrace(test: std::process::Output) {
     let mut it = err.lines();
 
     assert_eq!(it.next().map(|l| l.starts_with("thread '<unnamed>' panicked at")), Some(true));
-    assert_eq!(it.next(), Some("note: Run with `RUST_BACKTRACE=1` for a backtrace."));
+    assert_eq!(it.next(), Some("note: Run with `RUST_BACKTRACE=yes` for a backtrace."));
     assert_eq!(it.next().map(|l| l.starts_with("thread 'main' panicked at")), Some(true));
     assert_eq!(it.next(), None);
 }