Throw a "quit" on a KeyboardException in py-framefilter.c

If a C-c comes while the Python code for a frame filter is running, it
will be turned into a Python KeyboardException.  It seems good for
this to be treated like a GDB quit, so this patch changes
py-framefilter.c to notice this situation and call throw_quit in this
case.

gdb/ChangeLog
2018-03-26  Tom Tromey  <tom@tromey.com>

	* python/py-framefilter.c (throw_quit_or_print_exception): New
	function.
	(gdbpy_apply_frame_filter): Use it.

gdb/testsuite/ChangeLog
2018-03-26  Tom Tromey  <tom@tromey.com>

	* gdb.python/py-framefilter.exp: Add test for KeyboardInterrupt.
	* gdb.python/py-framefilter.py (name_error): New global.
	(ErrorInName.function): Use name_error.

gdb/testsuite/gdb.python/py-framefilter.exp

@@ -213,6 +213,12 @@ gdb_test_multiple "bt 1" $test {
     }
 }
 
+# Now verify that we can see a quit.
+gdb_test_no_output "python name_error = KeyboardInterrupt" \
+    "Change ErrorFilter to throw KeyboardInterrupt"
+gdb_test "bt 1" "Quit" "bt 1 with KeyboardInterrupt"
+
+
 # Test with no debuginfo
 
 # We cannot use prepare_for_testing as we have to set the safe-patch

gdb/testsuite/gdb.python/py-framefilter.py

@@ -134,13 +134,17 @@ class FrameElider ():
     def filter (self, frame_iter):
         return ElidingIterator (frame_iter)
 
+# This is here so the test can change the kind of error that is
+# thrown.
+name_error = RuntimeError
+
 # A simple decorator that gives an error when computing the function.
 class ErrorInName(FrameDecorator):
     def __init__(self, frame):
         FrameDecorator.__init__(self, frame)
 
     def function(self):
-        raise RuntimeError('whoops')
+        raise name_error('whoops')
 
 # A filter that supplies buggy frames.  Disabled by default.
 class ErrorFilter():