std: Tweak the std::env OsString/String interface

This commit tweaks the interface of the `std::env` module to make it more
ergonomic for common usage:

* `env::var` was renamed to `env::var_os`
* `env::var_string` was renamed to `env::var`
* `env::args` was renamed to `env::args_os`
* `env::args` was re-added as a panicking iterator over string values
* `env::vars` was renamed to `env::vars_os`
* `env::vars` was re-added as a panicking iterator over string values.

This should make common usage (e.g. unicode values everywhere) more ergonomic
as well as "the default". This is also a breaking change due to the differences
of what's yielded from each of these functions, but migration should be fairly
easy as the defaults operate over `String` which is a common type to use.

[breaking-change]

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/rt/backtrace.rs b/src/libstd/rt/backtrace.rs
index 2af5a486d0d..ced84d7551e 100644
--- a/src/libstd/rt/backtrace.rs
+++ b/src/libstd/rt/backtrace.rs
@@ -29,7 +29,7 @@ pub fn log_enabled() -> bool {
         _ => {}
     }
 
-    let val = match env::var("RUST_BACKTRACE") {
+    let val = match env::var_os("RUST_BACKTRACE") {
         Some(..) => 2,
         None => 1,
     };