Fix stat/lstat error checking in a few places.

closes #6929. Please review.
Yes, the output from below is related to the change in the paste.

-Erik

> On Jul 12, 2014, at 12:54 PM, Tibor Vass <notifications@github.com> wrote:
> 
> In utils/utils.go:
> 
> > @@ -889,8 +889,8 @@ func ValidateContextDirectory(srcPath string) error {
> >  			return err
> >  		}
> >  		// skip checking if symlinks point to non-existing files, such symlinks can be useful
> > -		lstat, _ := os.Lstat(filePath)
> > -		if lstat.Mode()&os.ModeSymlink == os.ModeSymlink {
> > +		lstat, err := os.Lstat(filePath)
> @erikh Does the test still fail? (That is, is the build still succeeding?)
> 
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