vsftpd: allow building with openssl via option

Closes Homebrew/homebrew#8476.

Signed-off-by: Charlie Sharpsteen <source@sharpsteen.net>

Formula/vsftpd.rb

@@ -5,10 +5,20 @@ class Vsftpd < Formula
   md5 '2ea5d19978710527bb7444d93b67767a'
   homepage 'https://security.appspot.com/vsftpd.html'
 
+  def options
+    [
+      ["--openssl", "build with OpenSSL"],
+    ]
+  end
+
   # Patch so vsftpd doesn't depend on UTMPX, and can't find OS X's PAM library.
   def patches; DATA; end
 
   def install
+    if ARGV.include? "--openssl"
+      inreplace "builddefs.h", "#undef VSF_BUILD_SSL", "#define VSF_BUILD_SSL"
+    end
+
     inreplace "defs.h", "/etc/vsftpd.conf", "#{etc}/vsftpd.conf"
     inreplace "tunables.c", "/etc", etc
     inreplace "tunables.c", "/var", var
@@ -19,6 +29,15 @@ class Vsftpd < Formula
     man5.install "vsftpd.conf.5"
     man8.install "vsftpd.8"
   end
+
+  def caveats
+    if ARGV.include? "--openssl"
+      return <<-EOD.undent
+        vsftpd was compiled with SSL support. To use it you must generate a SSL
+        certificate and set 'enable_ssl=YES' in your config file.
+      EOD
+    end
+  end
 end
 
 __END__