As the curl command-line tool now includes it's own version of strdup(),
for platforms that don't have it, fixed up the git respository Visual
Studio project file generator to not include the version from lib in the
tool project files, rather than having both lib\strdup.[c|h] and
src\tool_strdup.[c|h] present.
..when working from the git repository. This is particularly useful
for single development environments where the project files for all
supported versions of Visual Studio may not be required.
This shouldn't happen with the source files in the repository, but
fixed the output when there are spurious files lying around that
contain spaces. For example "pop3 - Copy.c"
By including the offending source file in the project files the user
can then see the file and remove it if necessary.
