Improve file operations

Hmm, why did I not use File.write before? Oh well, fixed.

lib/msf/ui/console/command_dispatcher/core.rb

@@ -495,7 +495,7 @@ class Core
 
         # Portable file truncation?
         if File.writable?(Msf::Config.history_file)
-          File.open(Msf::Config.history_file, 'w') {}
+          File.write(Msf::Config.history_file, '')
         end
 
         print_good('Command history and history file cleared')

lib/msf/ui/console/command_dispatcher/jobs.rb

@@ -139,7 +139,7 @@ module Msf
                 framework.jobs.each_key do |i|
                   framework.jobs.stop_job(i)
                 end
-                File.truncate(Msf::Config.persist_file,0) if File.exist?(Msf::Config.persist_file)
+                File.write(Msf::Config.persist_file, '') if File.writable?(Msf::Config.persist_file)
               when "-i"
                 # Defer printing anything until the end of option parsing
                 # so we can check for the verbose flag.