(shell-command-to-string): Make the buffer current

since output goes in current buffer.  Use shell-command-switch.

lisp/simple.el

@@ -945,7 +945,9 @@ In either case, the output is inserted after point (leaving mark after it)."
 (defun shell-command-to-string (command)
   "Execute shell command COMMAND and return its output as a string."
   (with-output-to-string
-    (call-process shell-file-name nil t nil "-c" command)))
+    (with-current-buffer
+      standard-output
+      (call-process shell-file-name nil t nil shell-command-switch command))))
 
 (defconst universal-argument-map
   (let ((map (make-sparse-keymap)))