version-check.pl: display version number for symbols

This script is the start of a helper tool that scans a source code and
outputs the most recent libcurl version it finds symbols for. Meaning
that if there's no conditions in the code, that's the earliest libcurl
version the scanned code requires.

It is not added to the Makefile.am yet as it is still a bit crude, but
I'm committing it to keep it and allow us to work on it.

docs/examples/version-check.pl

@@ -0,0 +1,69 @@
+#!/usr/bin/env perl
+
+open(S, "<../libcurl/symbols-in-versions") || die;
+
+my %doc;
+my %rem;
+while(<S>) {
+    if(/(^CURL[^ \n]*) *(.*)/) {
+        my ($sym, $rest)=($1, $2);
+        my @a=split(/ +/, $rest);
+
+        $doc{$sym}=$a[0]; # when it was introduced
+
+        if($a[2]) {
+            # this symbol is documented to have been present the last time
+            # in this release
+            $rem{$sym}=$a[2];
+        }
+    }
+
+}
+
+close(S);
+
+sub age {
+    my ($ver)=@_;
+
+    my @s=split(/\./, $ver);
+    return $s[0]*10000+$s[1]*100+$s[2];
+}
+
+my %used;
+open(C, "<$ARGV[0]") || die;
+
+while(<C>) {
+    if(/\W(CURL[_A-Z0-9v]+)\W/) {
+        #print "$1\n";
+        $used{$1}++;
+    }
+}
+
+close(C);
+
+sub sortversions {
+    my $r = age($doc{$a}) <=> age($doc{$b});
+    if(!$r) {
+        $r = $a cmp $b;
+    }
+    return $r;
+}
+
+my @recent = reverse sort sortversions keys %used;
+
+# the most recent symbol
+my $newsym = $recent[0];
+# the most recent version
+my $newver = $doc{$newsym}; 
+
+print "The scanned source uses these symbols introduced in $newver:\n";
+
+for my $w (@recent) {
+    if($doc{$w} eq $newver) {
+        printf "  $w\n";
+        next;
+    }
+    last;
+}
+
+