Add target/target.h

This adds target/target.h.  This file declares some functions that the
"common" code can use and that the clients must implement.  It also
changes code in common to use these functions.

gdb/
2014-07-31  Tom Tromey  <tromey@redhat.com>
	    Gary Benson  <gbenson@redhat.com>

	* target/target.h: New file.
	* Makefile.in (HFILES_NO_SRCDIR): Add target/target.h.
	* target.h: Include target/target.h.
	(target_resume, target_wait, target_stop, target_read_memory)
	(target_write_memory, non_stop): Don't declare.
	* target.c (target_read_uint32): New function.
	* common/agent.c: Include target/target.h.
	[!GDBSERVER]: Don't include target.h or infrun.h.
	(agent_get_helper_thread_id): Use target_read_uint32.
	(agent_run_command): Always use target_resume, target_stop,
	target_wait, target_write_memory, and target_read_memory.
	(agent_capability_check): Use target_read_uint32.

gdb/gdbserver/
2014-07-31  Tom Tromey  <tromey@redhat.com>
	    Gary Benson  <gbenson@redhat.com>

	* target.c (target_wait, target_stop, target_resume)
	(target_read_memory, target_read_uint32)
	(target_write_memory): New functions.
XXX
Add target/symbol.h, update users

This adds a new "target/symbol.h" file, that declares a symbol-lookup
function used by code in common.  It follows the usual pattern, where
clients of "common" have their own definitions of this function.  This
simplifies agent.c a bit.