add btFileUtils::toLower to convert a string (char*) to lower case

URDF import demo: add COLLADA .dae file support
add FiniteElementMethod demo, extracted from the OpenTissue library (under the zlib license)
don't crash if loading an invalid STL file
add comparison with Assimp for COLLADA file loading (disabled by default, to avoid library dependency)
Gwen: disable some flags that make the build incompatible

src/Bullet3Common/b3FileUtils.h

@@ -70,8 +70,9 @@ struct b3FileUtils
 		return oriptr;
 	}
 
+	
 
-	void extractPath(const char* fileName, char* path, int maxPathLength)
+	static void extractPath(const char* fileName, char* path, int maxPathLength)
 	{
 		const char* stripped = strip2(fileName, "/");
 		stripped = strip2(stripped, "\\");
@@ -97,6 +98,25 @@ struct b3FileUtils
 		}
 	}
 
+	static char toLowerChar(const char t)
+	{
+		if (t>=(char)'A' && t<=(char)'Z')
+			return t + ((char)'a' - (char)'A');
+		else
+			return t;
+	}
+
+
+	static void toLower(char* str)
+	{
+		int len=strlen(str);
+		for (int i=0;i<len;i++)
+		{
+			str[i] = toLowerChar(str[i]);
+		}
+	}
+
+
 	/*static const char* strip2(const char* name, const char* pattern)
 	{
 		size_t const patlen = strlen(pattern);