Use external mode for term when running key bindings

Prior to this fix, when key binding is a script command (i.e. not a
readline command), fish would run that key binding using fish's shell
tty modes. Switch to using the external tty modes. This re-fixes
issue #2214.

tests/pexpects/fg2.py

@@ -43,3 +43,31 @@ expect_prompt("has stopped")
 sendline("fg")
 sleep(0.1) # allow tty to transfer
 send("\x03")  # control-c to cancel it
+
+expect_prompt()
+sendline("jobs")
+expect_prompt("jobs: There are no jobs")
+
+# Regression test for #2214: foregrounding from a key binding works!
+sendline(r"bind \cr 'fg >/dev/null 2>/dev/null'")
+expect_prompt()
+sendline("$fish_test_helper print_stop_cont");
+sleep(0.2)
+
+send("\x1A") # ctrl-z
+expect_prompt("SIGTSTP")
+sleep(0.1)
+send("\x12") # ctrl-r, placing fth in foreground
+expect_str("SIGCONT")
+
+# Do it again.
+send("\x1A")
+expect_str("SIGTSTP")
+sleep(0.1)
+send("\x12")
+expect_str("SIGCONT")
+
+# End fth by sending it anything.
+send("\x12")
+sendline("derp")
+expect_prompt()