Fixed test environment for escaped test output.

- test-lib uses 'read -r' to parse the test session input literally, without interpretation of backslashes.
- FIX: Use quoting to maintain original whitespace (tabs and multiple spaces) from the test session input (instead of condensing into a single space).
- Using Bash instead of POSIX shell for t1340-listescapes.sh, so that the interpretation of escape sequences is not dependent on the POSIX shell being used.
- Changed Makefile so that the shell selected by the shebang line is actually used when invoking tests, not the POSIX shell.
- Above changes obsolete the multiple escaping of the test session data; now, the test session can actually be pasted as-is into a test script, even when it contains backslashes. (I.e. works as expected now.)

tests/test-lib.sh

@@ -527,7 +527,7 @@ test_todo_session () {
     cmd=""
     status=0
     > expect
-    while read line
+    while read -r line
     do
 	case $line in
 	">>> "*)
@@ -552,7 +552,7 @@ test_todo_session () {
 	    fi
 	    ;;
 	*)
-	    echo $line >> expect
+	    echo "$line" >> expect
 	    ;;
 	esac
     done