Sourcemap fixes

c85d4318b935968b7266136008cbcf55c0418772 fixes an issue minifying backbone.js. There is an off-by-one error when the keys of object literals are quoted strings.
```
{
   'some': 'thing'
// ^ Uglify says the 'some' token begins on this index, when it really is the next one
}
```
d051f29cacc4f47b71437b8f5afaa9ef7dc428f2 fixes an issue minifying lo-dash.
```
{
   '\n': 'newline'
//   ^ Sourcemap's "names" array contains a newline character and maps it here
//     when it should be mapping the escaped "\n" string
}
```