Breakpoint location parsing: always error instead of warning

Breakpoint location parsing: always error instead of warning

It's odd that when parsing a breakpoint or location number, we error out
in most cases, but warn in others.

  (gdb) disable 1-
  bad breakpoint number at or near: '1-'
  (gdb) disable -1
  bad breakpoint number at or near: '-1'
  (gdb) disable .foo
  bad breakpoint number at or near: '.foo'
  (gdb) disable foo.1
  Bad breakpoint number 'foo.1'
  (gdb) disable 1.foo
  warning: bad breakpoint number at or near '1.foo'

This changes GDB to always error out.  It required touching one testcase
that expected the warning.

gdb/ChangeLog:
2017-11-07  Pedro Alves  <palves@redhat.com>

	* breakpoint.c (extract_bp_number_and_location): Change return
	type to void.  Throw error instead of warning.
	(enable_disable_command): Adjust.

gdb/testsuite/ChangeLog:
2017-11-07  Pedro Alves  <palves@redhat.com>

	* gdb.base/ena-dis-br.exp: Don't expect "warning:".