Optimize location information.

1. Remove `markStart` and use local variables. 
2. Rearrange predicates to comply to distribution.

Benchmark by V8 shell (v3.22.24)
--------
Before:

|Source|	Size|	Time|	Time|	Time|	Average|
|:--:|--:|--:|--:|--:|--:|
|Underscore 1.5.2|42.50|5.18|5.36|5.29|5.28|
|Backbone 1.1.0|58.70|5.53|5.54|5.61|5.56|
|MooTools 1.4.5|156.70|47.83|46.02|45.74|46.53|
|jQuery 1.9.1|262.10|65.30|73.89|68.70|69.30|
|YUI 3.12.0|330.40|48.91|54.84|50.47|51.41|
|jQuery.Mobile 1.4.2|442.20|114.62|115.23|114.41|114.75|
|Angular 1.2.5|701.70|90.26|89.24|99.37|92.96|
|Total|1,994.30|377.63|390.12|389.59|385.78|

After:

|Source|	Size|	Time|	Time|	Time|	Average|
|:--:|--:|--:|--:|--:|--:|
|Underscore 1.5.2|42.5|4.07|4.03|4.42|4.17|
|Backbone 1.1.0|58.7|4.67|4.65|5.06|4.79|
|MooTools 1.4.5|156.7|19.39|22.48|23.61|21.83|
|jQuery 1.9.1|262.1|57.73|58.14|53.94|56.60|
|YUI 3.12.0|330.4|45.18|44.48|22.08|37.25|
|jQuery.Mobile 1.4.2|442.2|98.74|92.57|106.00|99.10|
|Angular 1.2.5|701.7|74.11|74.15|79.08|75.78|
|Total|1994.3|303.89|300.50|294.19|299.53|

Speed up: 28.80%