Support baseDir option

This pull adds the `baseDir` option which when set indicates the base directory that the JS will be served out of. This is useful when the JS files are found in a directory hierarchy on the file-system that doesn't match 1:1 with how the files are being served through connect.

The example below shows how this works:


    connect: {
      server: {
        options: {
          port: 8000,
          base: 'site/'
        }
      },
    },
   jasmine: {
      coverage: {
        src: 'site/js/**/*.js',
        options: {
          templateOptions: {
            template: require('grunt-template-jasmine-requirejs'),
            coverage: 'coverage/coverage.json',
            report: 'coverage',
            baseDir: 'site/',
            templateOptions: {
              requireConfigFile: 'site/js/app/core/config.js',
              requireConfig: {
                baseUrl: '.grunt/grunt-contrib-jasmine/site/js'
              }
            }
          },

          // Setting +replace+ to false ensures that grunt-template-jasmine-istanbul
          // will leave alone the path to the files in the generated +outfile+. If this
          // is set to true then the +outfile+ will contain bad references to files that
          // requireJS tries to load.
          replace: false
        }
      }
    }

The source file are found in the `site/` directory on the file-system but the connect server servers up `site/` as root so it's not necessary to keep `site/` in the generated src paths when the requireJS config gets read in, modified, and then written back out.