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

@@ -109,6 +109,7 @@ 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 num);
 	unsigned char concat(int num);
@@ -225,7 +226,6 @@ 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);