Add multibyte-support to ctype-locale backend.

* add actual converter methods MultibyteToWchar() and WcharToMultibyte()
  to locale backend and implement them in the ctype subpart
* add management code for maintaining converters referenced by mbstate_t

headers/private/libroot/locale/ICUCtypeData.h

@@ -30,9 +30,20 @@ public:
 			status_t			ToWCTrans(wint_t wc, wctrans_t transition,
 									wint_t& result);
 
+			status_t			MultibyteToWchar(wchar_t* wcOut, const char* mb,
+									size_t mbLength, mbstate_t* mbState,
+									size_t& lengthOut);
+			status_t			WcharToMultibyte(char* mbOut, wchar_t wc,
+									mbstate_t* mbState, size_t& lengthOut);
+
 			const char*			GetLanginfo(int index);
 
 private:
+			status_t			_GetConverterForMbState(mbstate_t* mbState,
+									ICUConverterRef& converterRefOut);
+
+			status_t			_DropConverterFromMbState(mbstate_t* mbState);
+
 			/*
 			 * The following arrays have 384 elements where the elements at
 			 * index -128..-2 mirror the elements at index 128..255 (to protect

headers/private/libroot/locale/ICULocaleBackend.h

@@ -41,6 +41,12 @@ public:
 	virtual	status_t			ToWCTrans(wint_t wc, wctrans_t transition,
 									wint_t& result);
 
+	virtual status_t			MultibyteToWchar(wchar_t* wcOut, const char* mb,
+									size_t mbLength, mbstate_t* mbState,
+									size_t& lengthOut);
+	virtual status_t			WcharToMultibyte(char* mbOut, wchar_t wc,
+									mbstate_t* mbState, size_t& lengthOut);
+
 	virtual	const char*			GetLanginfo(int index);
 
 	virtual	status_t			Strcoll(const char* a, const char* b, int& out);

headers/private/libroot/locale/LocaleBackend.h

@@ -123,6 +123,12 @@ public:
 	virtual	status_t			ToWCTrans(wint_t wc, wctrans_t transition,
 									wint_t& result) = 0;
 
+	virtual status_t			MultibyteToWchar(wchar_t* wcOut, const char* mb,
+									size_t mbLength, mbstate_t* mbState,
+									size_t& lengthOut) = 0;
+	virtual status_t			WcharToMultibyte(char* mbOut, wchar_t wc,
+									mbstate_t* mbState, size_t& lengthOut) = 0;
+
 	virtual	const char*			GetLanginfo(int index) = 0;
 
 	virtual	status_t			Strcoll(const char* a, const char* b,