Add support for guile 2.0.5.

Add support for guile 2.0.5.

	* guile/guile-internal.h (gdbscm_guile_major_version): Declare.
	(gdbscm_guile_minor_version, gdbscm_guile_micro_version): Declare.
	(gdbscm_guile_version_is_at_least): Declare.
	(gdbscm_scm_string_to_int): Declare.
	* guile/guile.c (gdbscm_guile_major_version): New global.
	(gdbscm_guile_minor_version, gdbscm_guile_micro_version): New globals.
	(guile_datadir): New static global.
	(gdbscm_guile_data_directory): New function.
	(initialize_scheme_side): Update.
	(misc_guile_functions): Add guile-data-directory.
	(initialize_gdb_module): Fetch guile version number.
	* guile/lib/gdb.scm: Remove call to add-to-load-path.
	* guile/lib/gdb/init.scm (%initialize!): Ditto.
	* guile/lib/gdb/boot.scm: Use guile-data-directory.
	* guile/scm-exception.c (gdbscm_print_exception_with_stack): Fix
	comments.
	* guile/scm-string.c (gdbscm_scm_string_to_int): New function.
	* guile/scm-utils.c (gdbscm_guile_version_is_at_least): New function.
	* guile/scm-value.c (gdbscm_value_to_string): Only call
	scm_port_conversion_strategy if Guile version >= 2.0.6.

	doc/
	* guile.texi (Guile Configuration): Document guile-data-directory.