libctf: add mechanism to prohibit most operations without a strtab

libctf: add mechanism to prohibit most operations without a strtab

We are about to add machinery that deduplicates a child dict's strtab
against its parent.  Obviously if you open such a dict but do not import its
parent, all strtab lookups must fail: so add an LCTF_NO_STR flag that is set
in that window and make most operations fail if it's not set.  (Two more
that will be set in future commits are serialization and string lookup
itself.)

Notably, not all symbol lookup is impossible in this window: you can still
look up by symbol index, as long as this dict is not using an indexed
strtypetab (which obviously requires string lookups to get the symbol name).

include/
	* ctf-api.h (_CTF_ERRORS) [ECTF_HASPARENT]: New.
        [ECTF_WRONGPARENT]: Likewise.
	(ECTF_NERR): Update.
        Update comments to note the new limitations on ctf_import et al.

libctf/
	* ctf-impl.h (LCTF_NO_STR): New.
	* ctf-create.c (ctf_rollback): Error out when LCTF_NO_STR.
	(ctf_add_generic): Likewise.
	(ctf_add_struct_sized): Likewise.
	(ctf_add_union_sized): Likewise.
	(ctf_add_enum): Likewise.
	(ctf_add_forward): Likewise.
	(ctf_add_unknown): Likewise.
	(ctf_add_enumerator): Likewise.
	(ctf_add_member_offset): Likewise.
	(ctf_add_variable): Likewise.
	(ctf_add_funcobjt_sym_forced): Likewise.
	(ctf_add_type): Likewise (on either dict).
	* ctf-dump.c (ctf_dump): Likewise.
	* ctf-lookup.c (ctf_lookup_by_name): Likewise.
	(ctf_lookup_variable): Likewise. Likewise.
	(ctf_lookup_enumerator): Likewise.
	(ctf_lookup_enumerator_next): Likewise.
	(ctf_symbol_next): Likewise.
	(ctf_lookup_by_sym_or_name): Likewise, if doing indexed lookups.
	* ctf-types.c (ctf_member_next): Likewise.
	(ctf_enum_next): Likewise.
	(ctf_type_aname): Likewise.
	(ctf_type_name_raw): Likewise.
	(ctf_type_compat): Likewise, for either dict.
	(ctf_member_info): Likewise.
	(ctf_enum_name): Likewise.
	(ctf_enum_value): Likewise.
	(ctf_type_rvisit): Likewise.
	(ctf_variable_next): Note that we don't need to test LCTF_NO_STR.