Add a utility upon which every other project is dependent, to copy the
config.h.vs file to the source root config.h. Because the target may
have changed outside of visual studio, I have disabled the dependency
check so the file will be copied with every build..
Use new compile flag WIN32_VS to add/change logic of sftp client and
sftp server codes so that MS Visual Studio 2015 compiler and runtime can
be used. opendir(), readdir(), closedir() directory APIs and basename()
API of Unix/Linux are implemented in Windows as they are not available
in Windows/VisualStudio C-runtime. win32_dirent.c and win32_dirent.h
files added as dirent.c and dirent.h are not available in Windows and we
do not want to affect mingW/gcc builds for Windows which have those
files available.
