* lib/install-sh: Don't incorrectly claim that this implementation

* lib/install-sh: Don't incorrectly claim that this implementation
can install only one file at a time.
(doit_exec): New var, for using 'exec' if possible, to save a process.
(test_mode, intermediate_mode): Remove.
(mode): Check for IFS or globbing characters in mode, since they might
cause weird behavior with the other changes below.  All later uses
of '"$mode"' changed to '$mode', since the ""s no longer matter.
Use octal modes if the invoker specifies an octal mode, and use
octal umask values if 'umask' outputs octal values; this is more
likely to work with older operating systems since Automake uses
octal modes, and also works around a bug with HP-UX 11.23
'mkdir -p -m u=rwx,g=rx,o=rx,u+wx' reported by Ralf Wildenhues in
<http://lists.gnu.org/archive/html/bug-automake/2006-06/msg00024.html>.
(cp_umask, mkdir_umask): New variables, to avoid
temporarily creating files or directories with too-permissive modes.
(mkdir_mode): Use the FreeBSD 'install' method for computing modes of
intermediate directories; this is safer.
(posix_mkdir): Also test mkdir -p -m ... by making a directory in
/tmp and checking the resulting mode with 'ls', to catch a bug in
HP-UX 11.23 and IRIX 6.5 mkdir reported by Ralf in the same message.
Use ':' for true, not 'true'; this is a bit faster on
traditional implementations.