Make String::concat(const char *, unsigned int) public

This method is useful when receiving data from external sources that
pass an explicit length instead of a NUL-terminated string.

Author: matthijskooijman

api/String.h

@@ -102,6 +102,7 @@ class String
 	// concatenation is considered unsucessful.
 	unsigned char concat(const String &str);
 	unsigned char concat(const char *cstr);
+	unsigned char concat(const char *cstr, unsigned int length);
 	unsigned char concat(char c);
 	unsigned char concat(unsigned char c);
 	unsigned char concat(int num);
@@ -218,7 +219,6 @@ class String
 	void init(void);
 	void invalidate(void);
 	unsigned char changeBuffer(unsigned int maxStrLen);
-	unsigned char concat(const char *cstr, unsigned int length);
 
 	// copy and move
 	String & copy(const char *cstr, unsigned int length);