Clean up a little CMDStager methods

lib/msf/core/exploit/cmdstager.rb

@@ -132,10 +132,17 @@ module Exploit::CmdStager
     print_status("Command Stager progress - %7s done (%d/%d bytes)" % [percent, sent, total])
   end
 
+  #
+  # Create an instance of the flavored stager
+  #
   def create_stager
     STAGERS[flavor].new(exe)
   end
 
+  #
+  # Guess the default decoder stub if there is one defined for
+  # the flavor
+  #
   def guess_decoder
     return nil unless STUBS.key?(flavor)
 
@@ -185,21 +192,20 @@ module Exploit::CmdStager
   end
 
   def guess_flavor
-    c_platform = nil
-    if target_platform.names.length == 1
-      c_platform = target_platform.names.first
-    end
+    return nil unless target_platform.names.length == 1
+    c_platform = target_platform.names.first
     case c_platform
-    when 'linux', 'Linux'
-      return :bourne
-    when 'osx', 'OSX'
-      return :bourne
-    when 'unix', 'Unix'
-      return :bourne
-    when 'win', 'Windows'
-      return :vbs
+    when /linux/i
+      :bourne
+    when /osx/i
+      :bourne
+    when /unix/i
+      :bourne
+    when /win/i
+      :vbs
+    else
+      nil
     end
-    return nil
   end
 
   def target_flavor
@@ -212,7 +218,6 @@ module Exploit::CmdStager
     target_flavor.nil? || target_flavor == flavor || target_flavor.include?(flavor)
   end
 
-
   #
   # Methods to override - not used internally
   #