Fixes for string.rep, string.byte, string.lower, and string.upper. Also

factor out negative index handling to separate function, posrelat (to
match C Lua). When converting numbers to strings, see if the double value
can be represented exactly as a long, and if so format the string as
an integer. With these changes the standard test case "strings.lua" runs
to line 104 (over half way through!), where it uses string.format.

src/main/java/lua/value/LDouble.java

@@ -15,7 +15,13 @@ public class LDouble extends LNumber {
 	}
 
 	public LString luaAsString() {
-		return LString.valueOf( m_value );
+		long l = (long) m_value;
+		if ( m_value == (double) l ) {
+			// TODO: is this a good idea?
+			return new LString( Long.toString( l ) );
+		} else {
+			return LString.valueOf( m_value );
+		}
 	}
 	
 	public boolean isInteger() {