Test no =breakpoint-modified is emitted for modifications from MI commands

As design, =breakpoint-modified isn't emitted when breakpoints are modified
by MI commands.  This patch is to add tests for this.

gdb/testsuite:

2014-02-08  Yao Qi  <yao@codesourcery.com>

	* gdb.mi/mi-breakpoint-changed.exp (test_insert_delete_modify): Test
	that no =breakpoint-modified is emitted when breakpoints are
	modified through MI commands.