Fix various warnings

Found while building on Debian 7

src/main.h

@@ -128,7 +128,7 @@ extern bool fPruneMode;
 /** Number of MiB of block files that we're trying to stay below. */
 extern uint64_t nPruneTarget;
 /** Block files containing a block-height within MIN_BLOCKS_TO_KEEP of chainActive.Tip() will not be pruned. */
-static const signed int MIN_BLOCKS_TO_KEEP = 288;
+static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
 
 // Require that user allocate at least 550MB for block & undo files (blk???.dat and rev???.dat)
 // At 1MB per block, 288 blocks = 288MB.
@@ -138,7 +138,7 @@ static const signed int MIN_BLOCKS_TO_KEEP = 288;
 // full block file chunks, we need the high water mark which triggers the prune to be
 // one 128MB block file + added 15% undo data = 147MB greater for a total of 545MB
 // Setting the target to > than 550MB will make it likely we can respect the target.
-static const signed int MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
+static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
 
 /** Register with a network node to receive its signals */
 void RegisterNodeSignals(CNodeSignals& nodeSignals);

src/rest.cpp

@@ -19,7 +19,7 @@
 using namespace std;
 using namespace json_spirit;
 
-static const int MAX_GETUTXOS_OUTPOINTS = 15; //allow a max of 15 outpoints to be queried at once
+static const size_t MAX_GETUTXOS_OUTPOINTS = 15; //allow a max of 15 outpoints to be queried at once
 
 enum RetFormat {
     RF_UNDEF,

src/txmempool.cpp

@@ -166,7 +166,7 @@ void CTxMemPool::removeCoinbaseSpends(const CCoinsViewCache *pcoins, unsigned in
                 continue;
             const CCoins *coins = pcoins->AccessCoins(txin.prevout.hash);
             if (fSanityCheck) assert(coins);
-            if (!coins || (coins->IsCoinBase() && nMemPoolHeight - coins->nHeight < COINBASE_MATURITY)) {
+            if (!coins || (coins->IsCoinBase() && ((signed long)nMemPoolHeight) - coins->nHeight < COINBASE_MATURITY)) {
                 transactionsToRemove.push_back(tx);
                 break;
             }