* choose.cc: Eliminate extra array throughout. Use element in package

* choose.cc: Eliminate extra array throughout.  Use element in package
structure instead.  Use pointers rather than array indexes where appropriate.
(set_action): New function to set next action based on current.
(choose_caption): New function.  Returns display caption.
(check_existence): Change arguments.  Use pointer to 'info' structure.
(set_existence): Use pointer rather than array index.
(default_trust): Use trusts enum for second argument.
(set_full_list): Honor exclude element in package structure.
(build_labels): Eliminate.
(base): Make global.  Use const char * argument.
(get_package_version): Eliminate.
(getpkgbyname): New function.
(read_installed_db): Use parse_filename to get version info.
* desktop.cc (make_passwd_group): Use getpkgbyname function.
* download.cc (get_file_size): const argument.
(do_download): Use is_download_action to determine when something should be
downloaded.
* filemanip.h: Add some functions.
* ini.cc (do_ini): Use NULL rather than 0 for pointer assignment.
* ini.h: Use enums for actions and trusts.
(is_download_action): New macro.
(is_upgrade_action): Ditto.
(is_uninstall_action): Ditto.
(struct Package): Add new fields.
* inilex.l (yylex): Detect new setup.ini options.
* iniparse.y: Declare new tokens.
(yyparse): Detect exclude keyword.  Fill out version field even if version ==
0.
(new_package): Use greater granularity when allocating package array to avoid
repeated calls to realloc.
* install.cc (exists): const argument.
(uninstall_one): Take pkg argument.
(install_one): Ditto.  Eliminate unneeded arguments which can be derived from
package info.
(do_install): Iterate over package array using a pointer.  Use
is_download_action to control when package should be downloaded.
* tar.cc (tar_open): const argument.
* tar.h: Refloect const argument.