fix/silence various compiler warnings.

* ifdef unused static functions
* brackets around assignment and comparision
* no return statement in function returning non-void
* boost concept_checks.hpp unused-local-typedefs

wscript

@@ -385,7 +385,7 @@ def set_compiler_flags (conf,opt):
             ('-Wall', '-Wpointer-arith', '-Wcast-qual', '-Wcast-align', '-Wno-unused-parameter'))
 
     c_flags.extend(('-Wstrict-prototypes', '-Wmissing-prototypes'))
-    cxx_flags.append('-Woverloaded-virtual')
+    cxx_flags.extend(('-Woverloaded-virtual', '-Wno-unused-local-typedefs))
 
     #
     # more boilerplate