* external.cc (cygwin_internal): Implement CW_ALLOC_DRIVE_MAP,

	* external.cc (cygwin_internal): Implement CW_ALLOC_DRIVE_MAP,
	CW_MAP_DRIVE_MAP, CW_FREE_DRIVE_MAP.
	* fhandler_process.cc: Include mount.h.
	(get_volume_path_names_for_volume_name): Move to mount.cc.
	(struct dos_drive_mappings): Ditto.
	* mount.cc (get_volume_path_names_for_volume_name): Move here.
	(dos_drive_mappings::dos_drive_mappings): Ditto.
	(dos_drive_mappings::fixup_if_match): Ditto.
	(dos_drive_mappings::~dos_drive_mappings): Ditto.
	* mount.h (class dos_drive_mappings): Declare her.
	* include/sys/cygwin.h (cygwin_getinfo_types): Add CW_ALLOC_DRIVE_MAP,
	CW_MAP_DRIVE_MAP, CW_FREE_DRIVE_MAP.
	* include/cygwin/version.h: Bump API minor number.