add fileOpenDialog and enable loading of urdf from GUI

(will add .bullet file support soon)
Uses native Windows (getFileOpenFileName) and Mac OSX NSOpenPanel,
on Linux using pipe popen to zenity)

src/Bullet3Common/b3FileUtils.h

@@ -16,11 +16,21 @@ struct b3FileUtils
 
 	bool findFile(const char* orgFileName, char* relativeFileName, int maxRelativeFileNameMaxLen)
 	{
-		
-			const char* prefix[]={"","./","./data/","../data/","../../data/","../../../data/","../../../../data/"};
+		FILE* f=0;
+		f = fopen(orgFileName,"rb");
+                if (f)
+                {
+			//printf("original file found: [%s]\n", orgFileName);
+			sprintf(relativeFileName,"%s", orgFileName);
+			fclose(f);
+			return true;
+		}
+
+		//printf("Trying various directories, relative to current working directory\n");	
+			const char* prefix[]={"./","./data/","../data/","../../data/","../../../data/","../../../../data/"};
 			int numPrefixes = sizeof(prefix)/sizeof(const char*);
 	
-			FILE* f=0;
+			f=0;
 			bool fileFound = false;
 			int result = 0;
 
@@ -79,11 +89,11 @@ struct b3FileUtils
 			path[len]=0;
 		} else
 		{
-#ifdef _WIN32
-		sprintf_s(path, maxPathLength,"");
-#else
-			sprintf(path, "");
-#endif
+			b3Assert(maxPathLength>0);
+			if (maxPathLength>0)
+			{
+				path[0] = 0;
+			}
 		}
 	}
 
@@ -103,4 +113,4 @@ struct b3FileUtils
 	*/
 
 };
-#endif //B3_FILE_UTILS_H
+#endif //B3_FILE_UTILS_H