doc system fix: when using __doc__ and define==false, extract just

the `__doc__` pieces to avoid repeating the rest of the surrounding
code (which might include method definitions).

base/docs/Docs.jl

@@ -519,21 +519,30 @@ more than one expression is marked then the same docstring is applied to each ex
 """
 :(Base.@__doc__)
 
-function __doc__!(meta, def::Expr)
+function __doc__!(meta, def::Expr, define=true)
     if isexpr(def, :block, 2) && def.args[1] == symbol("#doc#")
         # Convert `Expr(:block, :#doc#, ...)` created by `@__doc__` to an `@doc`.
         def.head = :macrocall
-        def.args = [symbol("@doc"), meta, def.args[end]]
-        true
+        def.args = [symbol("@doc"), meta, def.args[end], define]
+        (true, def)
     else
         found = false
+        ret = Expr(:block)
         for each in def.args
-            found |= __doc__!(meta, each)
+            f, ex = __doc__!(meta, each)
+            if f
+                found = true
+                push!(ret.args, ex)
+            end
+        end
+        if length(ret.args)==1
+            return (found, ret.args[1])
+        else
+            return (found, ret)
         end
-        found
     end
 end
-__doc__!(meta, def) = false
+__doc__!(meta, def, define=true) = (false, def)
 
 # Predicates and helpers for `docm` expression selection:
 
@@ -594,7 +603,7 @@ function docm(meta, ex, define = true)
     # Errors generated by calling `macroexpand` are passed back to the call site.
     isexpr(x, :error) ? esc(x) :
     # When documenting macro-generated code we look for embedded `@__doc__` calls.
-    __doc__!(meta, x) ? esc(x) :
+    (temp = __doc__!(meta, x, define); temp[1]) ? esc(define ? x : temp[2]) :
     # Any "basic" expression such as a bare function or module name or numeric literal.
     isbasicdoc(x) ? namedoc(meta, nothing, x) :