* dir.cc (mkdir): Check last path component for "..".

	* dir.cc (mkdir): Check last path component for "..".
	(rmdir): Don't check last path component for "..".
	* fhandler_disk_file.cc (fhandler_disk_file::rmdir): Drop kludge
	which tries to allow deleting the current working directory.
	* path.cc (has_dot_last_component): Add parameter to indicate testing
	for "..".  Take trailing slash into account.
	(symlink_info::posixify): Rely on cygheap->cwd.win32 having a
	useful value.
	(cwdstuff::init): Initialize cygheap->cwd with current working
	directory.  Change to windows_system_directory afterwards.
	(cwdstuff::set): Never call SetCurrentDirectory here.  Just check
	if changing into target directory would be allowed.  Add comment to
	explain why.
	* path.h (has_dot_last_component): Declare with second parameter.
	* pinfo.cc (pinfo::zap_cwd): Remove.
	(pinfo::exit): Drop call to zap_cwd.
	* pinfo.h (class pinfo): Remove declaration of zap_cwd.
	* spawn.cc (spawn_guts): Set current working directory for non-Cygwin
	child applications.  Drop call to zap_cwd.