src/txmempool.cpp: make numEntries a uint32_t

Don't ever serialize a size_t or long, their sizes are platform
dependent.

src/txmempool.cpp

@@ -337,7 +337,7 @@ public:
     void Write(CAutoFile& fileout) const
     {
         fileout << nBestSeenHeight;
-        fileout << history.size();
+        fileout << (uint32_t)history.size();
         BOOST_FOREACH(const CBlockAverage& entry, history)
         {
             entry.Write(fileout);
@@ -348,7 +348,7 @@ public:
     {
         int nFileBestSeenHeight;
         filein >> nFileBestSeenHeight;
-        size_t numEntries;
+        uint32_t numEntries;
         filein >> numEntries;
         if (numEntries <= 0 || numEntries > 10000)
             throw runtime_error("Corrupt estimates file. Must have between 1 and 10k entries.");