Translate PyExc_KeyboardInterrupt to gdb "quit"

Translate PyExc_KeyboardInterrupt to gdb "quit"

A while back I typed "info pretty-printers" with a large number of
printers installed, and I typed "q" to stop the pagination.  I noticed
that gdb printed a Python exception in this case.

It seems to me that, instead, quitting pagination (or control-c'ing a
Python command generally) should be handled the same way that gdb
normally handles a quit.

This patch implements this idea by changing gdbpy_handle_exception to
treat PyExc_KeyboardInterrupt specially.

gdb/ChangeLog
2018-12-27  Tom Tromey  <tom@tromey.com>

	* python/py-utils.c (gdbpy_handle_exception): Translate
	PyExc_KeyboardInterrupt to quit.

gdb/testsuite/ChangeLog
2018-12-27  Tom Tromey  <tom@tromey.com>

	* gdb.python/py-cmd.exp (test_python_inline_or_multiline): Add
	pagination test.