Tidy up and refactor plperl.c.

- Changed MULTIPLICITY check from runtime to compiletime.
    No loads the large Config module.
- Changed plperl_init_interp() to return new interp
    and not alter the global interp_state
- Moved plperl_safe_init() call into check_interp().
- Removed plperl_safe_init_done state variable
    as interp_state now covers that role.
- Changed plperl_create_sub() to take a plperl_proc_desc argument.
- Simplified return value handling in plperl_create_sub.
- Changed perl.com link in the docs to perl.org and tweaked
    wording to clarify that require, not use, is what's blocked.
- Moved perl code in large multi-line C string literal macros
    out to plc_*.pl files.
- Added a test2macro.pl utility to convert the plc_*.pl files to
    macros in a perlchunks.h file which is #included
- Simplifed plperl_safe_init() slightly
- Optimized pg_verifymbstr calls to avoid unneeded strlen()s.

Patch from Tim Bunce, with minor editing from me.

src/pl/plperl/text2macro.pl

@@ -0,0 +1,98 @@
+=head1 NAME
+
+text2macro.pl - convert text files into C string-literal macro definitions
+
+=head1 SYNOPSIS
+
+  text2macro [options] file ... > output.h
+
+Options:
+
+  --prefix=S   - add prefix S to the names of the macros
+  --name=S     - use S as the macro name (assumes only one file)
+  --strip=S    - don't include lines that match perl regex S
+
+=head1 DESCRIPTION
+
+Reads one or more text files and outputs a corresponding series of C
+pre-processor macro definitions. Each macro defines a string literal that
+contains the contents of the corresponding text file. The basename of the text
+file as capitalized and used as the name of the macro, along with an optional prefix.
+
+=cut
+
+use strict;
+use warnings;
+
+use Getopt::Long;
+
+GetOptions(
+	'prefix=s'  => \my $opt_prefix,
+	'name=s'    => \my $opt_name,
+	'strip=s'   => \my $opt_strip,
+	'selftest!' => sub { exit selftest() },
+) or exit 1;
+
+die "No text files specified"
+	unless @ARGV;
+
+print qq{
+/*
+ * DO NOT EDIT - THIS FILE IS AUTOGENERATED - CHANGES WILL BE LOST
+ * Written by $0 from @ARGV
+ */
+};
+
+for my $src_file (@ARGV) {
+
+	(my $macro = $src_file) =~ s/ .*? (\w+) (?:\.\w+) $/$1/x;
+
+	open my $src_fh, $src_file # not 3-arg form
+		or die "Can't open $src_file: $!";
+
+	printf qq{#define %s%s \\\n},
+		$opt_prefix || '',
+		($opt_name) ? $opt_name : uc $macro;
+	while (<$src_fh>) {
+		chomp;
+
+		next if $opt_strip and m/$opt_strip/o;
+
+		# escape the text to suite C string literal rules
+		s/\\/\\\\/g;
+		s/"/\\"/g;
+
+		printf qq{"%s\\n" \\\n}, $_;
+	}
+	print qq{""\n\n};
+}
+
+print "/* end */\n";
+
+exit 0;
+
+
+sub selftest {
+	my $tmp = "text2macro_tmp";
+	my $string = q{a '' '\\'' "" "\\"" "\\\\" "\\\\n" b};
+
+	open my $fh, ">$tmp.pl" or die;
+	print $fh $string;
+	close $fh;
+
+	system("perl $0 --name=X $tmp.pl > $tmp.c") == 0 or die;
+	open $fh, ">>$tmp.c";
+	print $fh "#include <stdio.h>\n";
+	print $fh "int main() { puts(X); return 0; }\n";
+	close $fh;
+	system("cat -n $tmp.c");
+	
+	system("make $tmp") == 0 or die;
+	open $fh, "./$tmp |" or die;
+	my $result = <$fh>;
+	unlink <$tmp.*>;
+
+	warn "Test string: $string\n";
+	warn "Result     : $result";
+	die "Failed!" if $result ne "$string\n";
+}