[binutils-gdb] Improve on-line help for thread_apply_command and thread_apply_all_command.

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 5c8f23cdab2a7cde2dae6fcd5f9b18d089efecaf ***

Author: Philippe Waroquiers <philippe.waroquiers@skynet.be>
Branch: master
Commit: 5c8f23cdab2a7cde2dae6fcd5f9b18d089efecaf

Improve on-line help for thread_apply_command and thread_apply_all_command.

Add a Usage: line for thread_apply_command, in particular to mention
the thread ID list.

In thread_apply_command and thread_apply_all_command help, use
uppercase for arg names, as this style seems to be more standard.

2018-04-20  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* thread.c (_initialize_thread): improve on-line help for
	thread_apply_command and thread_apply_all_command.