Increase max debug.log file size to 100MB

ZEC took the route of disabling this by default, so debug.log files grow without limit,
in attempt to gather more data about CVE-2019-16930, which was fixed in the same emergency
release as changing this default behavior.

KMD has chosen to ignore that ZEC change, which I find reasonable. We take the middle path,
and 10X increase the size limit.

Now debug.log must hit 100MB to be resized, and potentially lose some data about attacks.

src/util.cpp

@@ -892,7 +892,8 @@ void ShrinkDebugFile()
     // Scroll debug.log if it's getting too big
     boost::filesystem::path pathLog = GetDataDir() / "debug.log";
     FILE* file = fopen(pathLog.string().c_str(), "r");
-    if (file && boost::filesystem::file_size(pathLog) > 10 * 1000000)
+    unsigned int MAX_DEBUG_LOG_SIZE = 100*(1024*1024); // 100MB
+    if (file && boost::filesystem::file_size(pathLog) > MAX_DEBUG_LOG_SIZE )
     {
         // Restart the file with some of the end
         std::vector <char> vch(200000,0);