Pass database file name in function parameters

Storing it in a global variable with an unresolved symbol from libmandb
was never very clean, and caused linking complications on some
platforms.

Fixes Savannah bug #56734.

* libdb/mydbm.h (database): Remove external symbol.
* src/accessdb.c: Remove obsolete comment.
* src/catman.c (database): Remove global variable.
(parse_for_sec): Add database parameter.  Update all callers.
(main): Declare database locally.
* src/check_mandirs.c (gripe_rwopen_failed, testmandirs, update_db_time,
create_db, update_db, purge_missing): Add database parameter.  Update
all callers.
* src/check_mandirs.h (create_db, update_db, purge_missing): Update
prototypes.
* src/mandb.c (database): Remove global variable.
(update_one_file, update_db_wrapper): Add database parameter.  Update
all callers.
(mandb, process_manpath): Declare database locally.
* src/straycats.c (straycats): Add database parameter.  Update all
callers.
* src/whatis.c (database): Remove global variable.
(search): Declare database locally.
* include/manconfig.h.in (straycats): Update prototype.
* NEWS: Document this.