WIN32 MemoryTracking: track wcsdup() _wcsdup() and _tcsdup() usage

As of 25-mar-2013 wcsdup() _wcsdup() and _tcsdup() are only used in
WIN32 specific code, so tracking of these has not been extended for
other build targets. Without this fix, memory tracking system on
WIN32 builds, when using these functions, would provide misleading
results.

In order to properly extend this support for all targets curl.h
would have to define curl_wcsdup_callback prototype and consequently
wchar_t should be visible before that in curl.h.  IOW curl_wchar_t
defined in curlbuild.h and this pulling whatever system header is
required to get wchar_t definition.

Additionally a new curl_global_init_mem() function that also receives
user defined wcsdup() callback would be required.