Use ui_file_as_string in gdb/guile/

Use ui_file_as_string in gdb/guile/

gdb/ChangeLog:
2016-11-08  Pedro Alves  <palves@redhat.com>

	* guile/scm-breakpoint.c (gdbscm_breakpoint_commands): Use
	ui_file_as_string and adjust to use std::string.
	* guile/scm-disasm.c (gdbscm_arch_disassemble): Likewise.
	* guile/scm-frame.c (frscm_print_frame_smob): Likewise.
	* guile/scm-type.c (tyscm_type_name): Use ui_file_as_string and
	adjust to use std::string.  Throw exception directly instead of
	returning it in EXCP output parameter.
	(tyscm_print_type_smob, gdbscm_type_print_name): Adjust to
	tyscm_type_name interface change.
	* guile/scm-value.c (vlscm_print_value_smob, gdbscm_value_print):
	Use ui_file_as_string and std::string.