double-conversion floating-point conversions

- using double-conversion library for floating-point numeric/string
conversions
- added string replace[InPlace], remove[InPlace]
- reverted overwritten FileChannel purge age and count features
- file size value checks in SMTPClient

Foundation/testsuite/src/StringTest.h

@@ -65,6 +65,7 @@ public:
 
 	void testStringToInt();
 	void testStringToFloat();
+	void testStringToDouble();
 	void testStringToFloatError();
 	void testNumericLocale();
 	void benchmarkStrToFloat();