Windows CE support : using standard _WIN32_WCE flag instead of WINCE

- when compiling for Windows CE, a C++ project must define the preprocessor definitions: UNDER_CE=$(CEVersion),_WIN32_WCE=$(CEVersion)
- choosing the "_WIN32_CE" form for uniformization with "_WIN32" and "_WIN32_WINNT" already used in libzmq (boost is using both forms)
- see http://msdn.microsoft.com/en-us/library/ee479161(v=winembedded.60).aspx
Windows CE support : uncommenting #define EACCES needed

- tested for Windows CE 5.0 under Visual Studio 2008 Pro
- tested for Windows XP under Visual Studio 2008 Pro
Windows CE support : some more #if !defined _WIN32_WCE

- Windows CE does not manage security attributes (no SetSecurityDescriptorDacl(), SetEvent (NULL, xxx) ...)
- Windows CE does not inheritance of sockets for child process (SetHandleInformation ((HANDLE) *w_, HANDLE_FLAG_INHERIT...)
- see comments about story "Porting ZeroMQ to Windows Mobile" on webpage http://www.zeromq.org/story:5
Merge pull request #517 from SRombauts/master

Windows CE support : using standard _WIN32_WCE flag instead of WINCE