fix keyword lambda values by retaining statements in Result

As reported in issue #748, there was a bug in which passing a lambda
as the value of a :keyword argument would fail—

$ hy --spy
hy 0.10.1 using CPython(default) 3.4.0 on Linux
=> (sorted (range 10) :key (fn [x] (- x)))
from hy.core.language import range
sorted(range(10), key=_hy_anon_fn_1)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
NameError: name '_hy_anon_fn_1' is not defined

The function call would appear in the generated AST without being
preceded by the appropriate function definition corresponding to the
anonymous function argument value in the Hy source, causing either a
NameError (as in the example above), or erroneous reuse of whatever
function was already pointed to by the `_hy_anon_fn_` name referenced
in the list of keywords passed to `ast.Call`.

This commit aims to fix the problem by handling it in same way that
the expression/statement gap is bridged many other places in the
compiler, by adding the compiled value of the keyword argument to the
Result object being built during `_compile_collect`, with the
understanding that any Python statements implied by the argument value
will be appropriately preserved therein.

hy/compiler.py

@@ -462,6 +462,7 @@ class HyASTCompiler(object):
                     raise HyCompileError(msg.format(kw=str(expr)))
 
                 compiled_value = self.compile(value)
+                ret += compiled_value
 
                 # no unicode for py2 in ast names
                 keyword = str(expr[2:])

tests/native_tests/language.hy

@@ -1140,7 +1140,8 @@
   (assert (= (kwtest :key "value") {"key" "value"}))
   (assert (= (kwtest :key-with-dashes "value") {"key_with_dashes" "value"}))
   (assert (= (kwtest :result (+ 1 1)) {"result" 2}))
-  (assert (= (kwtest :key (kwtest :key2 "value")) {"key" {"key2" "value"}})))
+  (assert (= (kwtest :key (kwtest :key2 "value")) {"key" {"key2" "value"}}))
+  (assert (= ((get (kwtest :key (fn [x] (* x 2))) "key") 3) 6)))
 
 (defmacro identify-keywords [&rest elts]
   `(list