gdb_byte for binary buffer, char for string: common/agent.c.

gdb_byte for binary buffer, char for string: common/agent.c.

Similarly to the remote code, agent commands are mostly ascii.  Cast to
gdb_byte when treating the command buffer as raw memory bytes.

2013-04-19  Pedro Alves  <palves@redhat.com>

	* common/agent.c (agent_run_command): Add cast to gdb_byte *.