Remove dead code from installperl, related to a 5.000->5.001 change.

5.000 installed autosplit files into archlib. 5.001 and later install into
privlib. archlib is earlier in @INC. It wasn't until 5.005 that perl put the
version number into the paths used for privlib and archlib, hence without
special treatment, the files installed by 5.001 would not be found, because
those from 5.000 would be earlier in @INC.

See commit a841533b5cf319b3 (Oct 2009) which removes similar special casing
code dealing with perldiag.pod confusion between 5.003 and 5.004

All this code became redundant when 5.005 added the version number to
library paths. (strictly, commit bfb7748a896459cc in Jul 1998)
In installperl, invert the sense of the variable used for the -o option.

Previously it was $otherperls, and had to have its default of 1 explicitly
set. Change it to $skip_otherperls, and the default default of undef is
perfect.
In installperl, record the state of options in %opts instead of lexicals.

Replace all lexicals used to track the state of command line options with
entries in the hash %opts. Make an exception for $versiononly, as it is
controlled by 2 different command line options, and accessed in significantly
more places than the state of any other command line option.
In installperl rename $opt{dostrip} to $opt{strip}.

This will provide a more meaningful long option name once installperl is
converted to Getopt::Long.
Convert installperl to use Getopt::Long.

This requires some special handling for the +v option. Fortunately, we can
cheat, because we know that no other non-options are acceptable. This does
change the behaviour slightly from before:

* single letter options now also have long names
* invalid options are now rejected
* command line arguments that are not options are now rejected

However, the behaviour for all valid documented invocations is unchanged.

Also, add a --help option to display the usage message.
Refactor installman's option handling to use Getopt::Long's "multiple names".

Previously installman specified synonyms for options as distinct
options, and then used explicit code to merge them.

Also add -h and -? as synonyms for --help.
Add a no-op option --strip to installman.

This intentionally does nothing.

--strip for installperl instructs it to strip the installed binaries. Hence
by permitting installman to accept --strip without error Makefile.SH can be
simplified, as it's possible to pass identical flags to both install scripts.
Refactor the Makefile so that the install target depends on install-all.

Also, add targets install_notify and install-notify, as synonyms for
no_install and no-install. Previously install, install-all and install_all
were all generated by the same rule.

These changes make future refactoring easier.
In Makefile.SH, use the long names for options passed to install{perl,man}

This makes it clearer what is going on, and enables a simplifying refactoring.
Refactor Makefile.SH to generate the install-* targets in a loop.

This slightly reduces the line count, merges five-fold duplication into one,
and works toward removing 5 recursive calls from Makefile to itself.
Inline the Makefile rule for extra.install into all 6 targets which use it.

This eliminates 6 recursive calls from Makefile to itself. As five of these
are generated from a loop in Makefile.SH, this isn't massive code
duplication. It's not obvious how to merge the sixth without increasing the
code complexity.

Additionally, if the user has specified extra modules to download and build
from CPAN using Configure's -Dextra, this avoids building perl, the non-XS
modules and the CPAN modules twice on make install.
Don't call CPAN to install and "extra" modules for the install-notify target.

Previously the Makefile's install-notify target built extra.install just like
the other 5 install targets. However, the other 5 actually install perl,
whereas install-notify (a.k.a. no-install) runs installperl and installman
with the --notify option (formerly -n), to cause them to print what they would
do but take no action. Hence if -Dextras was used, make no-install would
actually install the extra modules, but nothing else. This is inconsistent.