gdb/doc/

gdb/doc/
	* gdb.texinfo (Maintenance Commands): Document "maint set dwarf2
	max-cache-age" and "maint show dwarf2 max-cache-age".
gdb/
	* Makefile.in (dwarf2read.o): Update dependencies.
	* dwarf2read.c: Include "command.h" and "gdbcmd.h".
	(struct dwarf2_per_objfile): Add all_comp_units, n_comp_units,
	and read_in_chain.
	(struct dwarf2_cu): Add read_in_chain, per_cu, last_used,
	mark, and has_form_ref_addr.
	(struct dwarf2_per_cu_data): New.
	(dwarf2_max_cache_age): New.
	(dwarf2_build_psymtabs_hard): Free cached compilation units
	after loading.  Create and manage the list of compilation units.
	Remove unnecessary NULL initialization.  Fix indentation.
	(psymtab_to_symtab_1): Initialize all of CU.
	(dwarf2_read_abbrevs): Set has_form_ref_addr.
	(find_partial_die): Use dwarf2_find_containing_comp_unit
	and load_comp_unit.
	(free_stack_comp_unit): Update comments.  Clear the per-cu
	pointer.  Handle aging.
	(dwarf2_find_containing_comp_unit, free_cached_comp_units)
	(age_cached_comp_units, free_one_cached_comp_unit)
	(dwarf2_mark, dwarf2_clear_marks, create_all_comp_units)
	(load_comp_unit, dwarf2_find_comp_unit, free_one_comp_unit)
	(set_dwarf2_cmdlist, show_dwarf2_cmdlist, set_dwarf2_cmd)
	(show_dwarf2_cmd): New.
	(_initialize_dwarf2_read): Provide "maint set dwarf2 max-cache-age"
	and "maint show dwarf2 max-cache-age".
	* gdbcmd.h (maintenance_set_cmdlist, maintenance_show_cmdlist): New
	externs.
	* maint.c (maintenance_set_cmdlist, maintenance_show_cmdlist): Make
	global.