Prepend unlink instead of appending

Makes it work when using meterpreter.  Because "quit" or "exit" in the
console ends up calling die() instead of falling through to whatever's
left in the file, a meterpreter session would never reach the code to
delete itself before this change.

lib/msf/core/exploit/php_exe.rb

@@ -50,7 +50,7 @@ module Exploit::PhpEXE
 			end
 			if target["Platform"] == 'win'
 				bin_name << ".exe"
-				print_debug("Unable to clean up #{bin_name}, delete it manually")
+				print_warning("Unable to clean up #{bin_name}, delete it manually")
 			end
 			p = Rex::Text.encode_base64(generate_payload_exe)
 			php = %Q{
@@ -74,7 +74,9 @@ module Exploit::PhpEXE
 		end
 
 		if opts[:unlink_self]
-			php << "unlink(__FILE__);"
+			# Prepend instead of appending to make sure it happens no matter
+			# what the payload normally does.
+			php = "@unlink(__FILE__);" + php
 		end
 
 		php.gsub!(/#.*$/, '')