Refresh the thinking of --prefix and --openssldir

--prefix is now exclusively used for software and manual installation.
--openssldir is not exclusively used as a default location for certs,
keys and the default openssl.cnf.

This change is made to bring clarity, to have the two less
intertwined, and to be more compatible with the usual ways of software
installation.

Please change your habits and scripts to use --prefix rather than
--openssldir for installation location now.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>

Configure

diff --git a/Configure b/Configure
index 5189fcb..4c2f01f 100755
--- a/Configure
+++ b/Configure
@@ -21,10 +21,15 @@
 # --config      add the given configuration file, which will be read after
 #               any "Configurations*" files that are found in the same
 #               directory as this script.
-# --openssldir  install OpenSSL in OPENSSLDIR (Default: DIR/ssl if the
-#               --prefix option is given; /usr/local/ssl otherwise)
-# --prefix      prefix for the OpenSSL include, lib and bin directories
-#               (Default: the OPENSSLDIR directory)
+# --prefix      prefix for the OpenSSL installation, which includes the
+#               directories bin, lib, include, share/man, share/doc/openssl
+#               This becomes the value of INSTALLTOP in Makefile
+#               (Default: /usr/local)
+# --openssldir  OpenSSL data area, such as openssl.cnf, certificates and keys.
+#               If it's a relative directory, it will be added on the directory
+#               given with --prefix.
+#               This becomes the value of OPENSSLDIR in Makefile and in C.
+#               (Default: PREFIX/ssl)
 #
 # --install_prefix  Additional prefix for package builders (empty by
 #               default).  This needn't be set in advance, you can
@@ -1056,8 +1061,6 @@
 $exe_ext=".exe" if ($target eq "Cygwin" || $target eq "DJGPP" || $target =~ /^mingw/);
 $exe_ext=".nlm" if ($target =~ /netware/);
 $exe_ext=".pm"  if ($target =~ /vos/);
-$openssldir="/usr/local/ssl" if ($openssldir eq "" and $prefix eq "");
-$prefix=$openssldir if $prefix eq "";
 
 $default_ranlib= &which("ranlib") or $default_ranlib="true";
 $perl=$ENV{'PERL'} or $perl=&which("perl5") or $perl=&which("perl")
@@ -1066,11 +1069,10 @@
 
 $cross_compile_prefix=$ENV{'CROSS_COMPILE'} if $cross_compile_prefix eq "";
 
-chop $openssldir if $openssldir =~ /\/$/;
-chop $prefix if $prefix =~ /.\/$/;
-
-$openssldir=$prefix . "/ssl" if $openssldir eq "";
-$openssldir=$prefix . "/" . $openssldir if $openssldir !~ /(^\/|^[a-zA-Z]:[\\\/])/;
+$prefix = "/usr/local" if !$prefix;
+$openssldir = "ssl" if !$openssldir;
+$openssldir = catdir($prefix, $openssldir)
+    unless file_name_is_absolute($openssldir);
 
 
 print "IsMK1MF=$IsMK1MF\n";