Compile with extra warnings turned on. And more makefile/code tidying up.

This turns on most gcc warnings, and removes some unused variables and other code that triggers warnings.
Exceptions are:
 -Wno-sign-compare : triggered by lots of comparisons of signed integer to foo.size(), which is unsigned.
 -Wno-char-subscripts : triggered by the convert-to-hex functions (I may fix this in a future commit).

src/serialize.h

@@ -89,6 +89,7 @@ enum
         const bool fRead = false;               \
         unsigned int nSerSize = 0;              \
         ser_streamplaceholder s;                \
+        assert(fGetSize||fWrite||fRead); /* suppress warning */ \
         s.nType = nType;                        \
         s.nVersion = nVersion;                  \
         {statements}                            \
@@ -102,6 +103,7 @@ enum
         const bool fWrite = true;               \
         const bool fRead = false;               \
         unsigned int nSerSize = 0;              \
+        assert(fGetSize||fWrite||fRead); /* suppress warning */ \
         {statements}                            \
     }                                           \
     template<typename Stream>                   \
@@ -112,6 +114,7 @@ enum
         const bool fWrite = false;              \
         const bool fRead = true;                \
         unsigned int nSerSize = 0;              \
+        assert(fGetSize||fWrite||fRead); /* suppress warning */ \
         {statements}                            \
     }