Visual Studio -- rename project and solution files

All of the project and solution files for building the SpiderMonkey
version of MongoDB executables have been renamed to their old names
plus "_sm", and all of the previously "_v8" tagged files are renamed
to their base names (e.g. mongod_v8.sln is renamed to mongod.sln).
This is consistent with V8 being the default JavaScript engine, with
an option to build a SpiderMonkey version.  Also added new "master"
solution files as src/mongodb.sln to build components for the V8
version and src/mongodb_sm.sln to build for SpiderMonkey.  Please
delete existing target build directories (e.g. src/mongo/db/x64/Debug)
before rebuilding with the updated project files.