HexStr: don't build a vector<char> first

Also const correctness for lookup tables in hex functions throughout the code.

src/bignum.h

@@ -305,7 +305,7 @@ public:
             psz++;
 
         // hex string to bignum
-        static signed char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
+        static const signed char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
         *this = 0;
         while (isxdigit(*psz))
         {

src/uint256.h

@@ -306,7 +306,7 @@ public:
             psz += 2;
 
         // hex string to uint
-        static unsigned char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
+        static const unsigned char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
         const char* pbegin = psz;
         while (phexdigit[(unsigned char)*psz] || *psz == '0')
             psz++;

src/util.cpp

@@ -424,7 +424,7 @@ bool ParseMoney(const char* pszIn, int64& nRet)
 }
 
 
-static signed char phexdigit[256] =
+static const signed char phexdigit[256] =
 { -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
   -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
   -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,

src/util.h

@@ -256,9 +256,9 @@ inline int64 abs64(int64 n)
 template<typename T>
 std::string HexStr(const T itbegin, const T itend, bool fSpaces=false)
 {
-    std::vector<char> rv;
-    static char hexmap[16] = { '0', '1', '2', '3', '4', '5', '6', '7',
-                               '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
+    std::string rv;
+    static const char hexmap[16] = { '0', '1', '2', '3', '4', '5', '6', '7',
+                                     '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
     rv.reserve((itend-itbegin)*3);
     for(T it = itbegin; it < itend; ++it)
     {
@@ -269,7 +269,7 @@ std::string HexStr(const T itbegin, const T itend, bool fSpaces=false)
         rv.push_back(hexmap[val&15]);
     }
 
-    return std::string(rv.begin(), rv.end());
+    return rv;
 }
 
 inline std::string HexStr(const std::vector<unsigned char>& vch, bool fSpaces=false)