Add support for alternate TLs implementations.

test.sh

@@ -4,11 +4,9 @@ set -eu
 export RUST_BACKTRACE=1
 export RUSTFLAGS="-D dead_code -D unused-variables -D unused"
 
-for tls in "" tls ; do
-  for feature in "" json charset cookies socks-proxy native-certs ; do
-    if ! cargo test --no-default-features --features "${tls} ${feature}" ; then
-      echo Command failed: cargo test \"${what}\" --no-default-features --features \"${tls} ${feature}\"
-      exit 1
-    fi
-  done
+for feature in "" tls json charset cookies socks-proxy "tls native-certs" native-tls; do
+  if ! cargo test --no-default-features --features "${feature}" ; then
+    echo Command failed: cargo test --no-default-features --features \"${feature}\"
+    exit 1
+  fi
 done