std: Fix env() assert when an environment variable's value contains a '=' char

Author: cpeterso

src/libstd/generic_os.rs

@@ -21,7 +21,7 @@ fn setenv(n: str, v: str) { }
 fn env() -> [(str,str)] {
     let pairs = [];
     for p in os::rustrt::rust_env_pairs() {
-        let vs = str::split_char(p, '=');
+        let vs = str::splitn_char(p, '=', 1u);
         assert vec::len(vs) == 2u;
         pairs += [(vs[0], vs[1])];
     }