* Finish basic read-write support for SOM archive libraries. Bugs

	* Finish basic read-write support for SOM archive libraries.  Bugs
	surely remain as this hasn't been tested all that much.
	* som.c (SOM_LST_HASH_SIZE, SOM_LST_MODULE_LIMIT): Define.
	(struct som_misc_symbol_info): New structure to hold info necessary
	to build both normal and library symbol tables.
	(som_derive_misc_symbol_info): New function to derive info necessary
	to build both normal and library symbol tables.
	(som_build_and_write_symbol_table): Use new function to derive misc
	symbol information.
	(som_slurp_symbol_table): Update backend private data for symbols
	appropriately.
	(som_bfd_prep_for_ar_write): New function.
	(som_bfd_ar_symbol_hash): New function.
	(som_bfd_ar_write_symbol_stuff): New function.
	(som_write_armap): Flesh out.
	(som_vec): Fix ar padding character.

	* som.c: Consistently use memset rather than bzero.