Fix bug in dwarf-mode.el

Fix bug in dwarf-mode.el

I noticed that, occasionally, dwarf-mode would think that the objdump
subprocess was still running after it had clearly exited.  I managed
to reliably reproduce this today and learned that a process sentinel
is not guaranteed to be run with the current buffer set to the process
buffer.  This patch fixes the problem.

I've bumped the version number of dwarf-mode.el to make it easier to
install for users who already have an earlier one installed.

I'm checking this in.

2022-03-15  Tom Tromey  <tromey@adacore.com>

	* dwarf-mode.el: Now 1.7.
	(dwarf--sentinel): Switch to the process buffer.