[SPARK-5664][BUILD] Restore stty settings when exiting from SBT's spark-shell

For launching spark-shell from SBT.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #4451 from viirya/restore_stty and squashes the following commits:

fdfc480 [Liang-Chi Hsieh] Restore stty settings when exit (for launching spark-shell from SBT).

build/sbt

@@ -125,4 +125,32 @@ loadConfigFile() {
 [[ -f "$etc_sbt_opts_file" ]] && set -- $(loadConfigFile "$etc_sbt_opts_file") "$@"
 [[ -f "$sbt_opts_file" ]] && set -- $(loadConfigFile "$sbt_opts_file") "$@"
 
+exit_status=127
+saved_stty=""
+
+restoreSttySettings() {
+  stty $saved_stty
+  saved_stty=""
+}
+
+onExit() {
+  if [[ "$saved_stty" != "" ]]; then
+    restoreSttySettings
+  fi
+  exit $exit_status
+}
+
+saveSttySettings() {
+  saved_stty=$(stty -g 2>/dev/null)
+  if [[ ! $? ]]; then
+    saved_stty=""
+  fi
+}
+
+saveSttySettings
+trap onExit INT
+
 run "$@"
+
+exit_status=$?
+onExit

build/sbt-launch-lib.bash

@@ -81,7 +81,7 @@ execRunner () {
     echo ""
   }
 
-  exec "$@"
+  "$@"
 }
 
 addJava () {