Add a newline in output messages

Hi,
GDB prints two warnings in one single line, as below:

 (gdb) p 1.2
 $1 = 1.2
 (gdb) enable $1.2
 History value must have integer type.Bad breakpoint number '$1'

This patch adds '\n' at the end of message.

gdb:

2014-03-06  Yao Qi  <yao@codesourcery.com>

	* cli/cli-utils.c (get_number_trailer): Add '\n' at the end of
	message.