Revert "startup: use path.resolve instead of path.join(cwd, ...)"

This reverts commit b0c1541.

Reverted commit introduced a regression causing `process.argv[0]` to be
invalid in node processes spawned from `PATH` (without explicit path to
executable file - for example when using global node installation).

Instead of finding a correct path to the executable, `process.cwd()`
would be prepended to `process.argv[0]`.

src/node.js

@@ -433,14 +433,18 @@
 
   startup.resolveArgv0 = function() {
     var cwd = process.cwd();
+    var isWindows = process.platform === 'win32';
 
     // Make process.argv[0] into a full path, but only touch argv[0] if it's
     // not a system $PATH lookup.
     // TODO: Make this work on Windows as well.  Note that "node" might
     // execute cwd\node.exe, or some %PATH%\node.exe on Windows,
     // and that every directory has its own cwd, so d:node.exe is valid.
-    var path = NativeModule.require('path');
-    process.argv[0] = path.resolve(process.argv[0]);
+    var argv0 = process.argv[0];
+    if (!isWindows && argv0.indexOf('/') !== -1 && argv0.charAt(0) !== '/') {
+      var path = NativeModule.require('path');
+      process.argv[0] = path.join(cwd, process.argv[0]);
+    }
   };
 
   // Below you find a minimal module system, which is used to load the node