Wrap create_directory calls in try...catch blocks.

Ignores any exceptions thrown if directory exists, otherwise re-throws exception.

Rebased-By: Wladimir J. van der Laan <laanwj@gmail.com>

src/util.cpp

@@ -976,7 +976,7 @@ boost::filesystem::path GetDefaultDataDir()
 #ifdef MAC_OSX
     // Mac
     pathRet /= "Library/Application Support";
-    fs::create_directory(pathRet);
+    TryCreateDirectory(pathRet);
     return pathRet / "Bitcoin";
 #else
     // Unix
@@ -1090,6 +1090,23 @@ bool RenameOver(boost::filesystem::path src, boost::filesystem::path dest)
 #endif /* WIN32 */
 }
 
+
+// Ignores exceptions thrown by boost's create_directory if the requested directory exists.
+//   Specifically handles case where path p exists, but it wasn't possible for the user to write to the parent directory.
+bool TryCreateDirectory(const boost::filesystem::path& p)
+{
+    try
+    {
+        return boost::filesystem::create_directory(p);
+    } catch (boost::filesystem::filesystem_error) {
+        if (!boost::filesystem::exists(p) || !boost::filesystem::is_directory(p))
+            throw;
+    }
+
+    // create_directory didn't create the directory, it had to have existed already
+    return false;
+}
+
 void FileCommit(FILE *fileout)
 {
     fflush(fileout); // harmless if redundantly called