Unwrap director classes only when returning a pointer or reference to an object

This involves properly counting the number of references and pointers in the return
type of a function and only generate unwrapping code if this number is 1.
For template instances some post-processing code is added to fix the 'decl' and
'type' attributes of functions if changed in an unfavorable way during template
expansion.
This commit fixes swig#1811.

Examples/test-suite/common.mk

@@ -213,6 +213,7 @@ CPP_TEST_CASES += \
 	director_smartptr \
 	director_thread \
 	director_unroll \
+	director_unwrap_result \
 	director_using \
 	director_void \
 	director_wombat \