Consistency of configure generated config.h

In an attempt to minimize the differences inherent to the various Windows ports (THRIFT-923, THRIFT-1123, THRIFT-1031, THRIFT-591...), and to fix some inconsistencies related to the inclusion of config.h, enclosed is a patch over current trunk which attempts to reconcile the usage of the configure generated file.

Due to my lack of knowledge about the thrift code base, the patch is probably incomplete and does apply only to the thrift/thriftnb C++ libraries, ignoring the other C++ components (compiler, test...).

Side note: This patch is part of an attempt to maintain a Windows port for thriftnb (https://github.com/aubonbeurre/thrift/blob/winthriftnb-0.8.x/README.non.blocking.Windows)

Tested on Ubuntu and Windows.