Extending QDate, QTime and QDateTime

[jamadagni]

Am trying another approach. I will modify the qdatetime.cpp qdatetime.h qdatetime_p.h files only and introduce them into the 4.11 source and compile and install it.

See the licence notice at the top of the files to see what has been changed.

One problem: handling negative years while converting to and from strings is going to be a problem. So wherever you find 1752 in the source file has not yet been converted. Your help in fixing the string conversion is most appreciated.