Add signed char keyword

On PowerPC and PowerPC64 systems, 'char' is unsigned by default.
Can be reproduced by using the -funsigned-char flag for gcc.
Adding the signed keyword adds compatibility on these systems.

Signed-off by: Jonathan Scruggs <j.scruggs@gmail.com>

COLLADABaseUtils/src/COLLADABUURI.cpp

@@ -32,7 +32,7 @@ namespace COLLADABU
 
 
 
-	const char HEX2DEC[256] = 
+	const signed char HEX2DEC[256] = 
 	{
 		/*       0  1  2  3   4  5  6  7   8  9  A  B   C  D  E  F */
 		/* 0 */ -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
@@ -107,9 +107,9 @@ namespace COLLADABU
 		{
 			if (*pSrc == '%')
 			{
-				char dec1, dec2;
-				if (    (char)(-1) != (dec1 = HEX2DEC[*(pSrc + 1)])
-				     && (char)(-1) != (dec2 = HEX2DEC[*(pSrc + 2)]))
+				signed char dec1, dec2;
+				if (    (signed char)(-1) != (dec1 = HEX2DEC[*(pSrc + 1)])
+				     && (signed char)(-1) != (dec2 = HEX2DEC[*(pSrc + 2)]))
 				{
 					*pEnd++ = (dec1 << 4) + dec2;
 					pSrc += 3;
@@ -222,14 +222,14 @@ namespace COLLADABU
 		}
 		else
 		{
-			mUriString = copyFrom_.mUriString;
-			mOriginalURIString = copyFrom_.mOriginalURIString;
-			mScheme = copyFrom_.mScheme;
-			mAuthority = copyFrom_.mAuthority;
-			mPath = copyFrom_.mPath;
-			mQuery = copyFrom_.mQuery;
-			mFragment = copyFrom_.mFragment;
-			mIsValid = copyFrom_.mIsValid;
+			mUriString = copyFrom_.mUriString;
+			mOriginalURIString = copyFrom_.mOriginalURIString;
+			mScheme = copyFrom_.mScheme;
+			mAuthority = copyFrom_.mAuthority;
+			mPath = copyFrom_.mPath;
+			mQuery = copyFrom_.mQuery;
+			mFragment = copyFrom_.mFragment;
+			mIsValid = copyFrom_.mIsValid;
 		}
 	}