Fix to suppress redcloth warning if gems not available

Minor doco fixes for set_local and friends

Rakefile

@@ -10,6 +10,8 @@ require 'tsort'
 begin
   require 'rubygems'
 rescue LoadError
+  # Don't show RedCloth warning if gems aren't available
+  $redcloth_available = false
 end
 
 task :default => :build

doc/vm/op_codes/set_local.yaml

@@ -8,10 +8,12 @@ stack_before:
   - value
   - ...
 stack_after:
+  - value
   - ...
 description: >-
-  Pops a value off the stack, and uses it to set the value of the local variable
-  identified by the literal _locl_.
+  Pops _value_ off the stack, and uses it to set the value of the local variable
+  identified by the literal _locl_. The value is then pushed back onto the stack,
+  to represent the return value from the expression.
 source: |-
     next_int;
     t1 = stack_pop();

doc/vm/op_codes/set_local_depth.yaml

@@ -11,10 +11,9 @@ stack_after:
   - value
   - ...
 description: >-
-  Uses the value on the top of the stack to update the value of the local variable
-  _local_ in an enclosing scope.
-
-  The top of the stack is *not* popped by this operation.
+  Uses the _value_ on the top of the stack to update the value of the local variable
+  _local_ in an enclosing scope. The value is then pushed back onto the stack, to
+  represent the return value from the expression.
 example: |-
   foo.each do |i|
     bar.each do |j|

doc/vm/op_codes/set_local_fp.yaml

@@ -11,10 +11,9 @@ stack_after:
   - value
   - ...
 description: >-
-  Uses the value on the top of the stack to update the value of the local variable
-  identified by _idx_.
-    
-  The top of the stack is *not* popped by this operation.    
+  Uses the _value_ on the top of the stack to update the value of the local variable
+  allocated on the stack, identified by _idx_. The value is left on the stack, to
+  represent the return value from the expression.
 notes:
   Local variables that are used within a method and not captured are allocated
   on the stack. This operation updates such a local from the current top of the