SERVER-5099 Convert Unicode text on Windows command line for all tools

For the Windows version of mongobridge, bsondump, docgenerator, mongodump,
mongoexport, mongofiles, mongoimport, loadgenerator, mongooplog,
mongorestore, mongosniff, mongostat, and mongotop, switch to a Unicode
"wmain()" entry point and convert Unicode characters on the command line
to UTF-8.  Move previous main() to a new toolMain() routine so it can be
called from both main() and wmain().  Clean up headers.