Don't draw lines for consecutive explicit "moveto" commands

With #1365 I didn't notice Fabric was rendering lines for consecutive M/m path commands. Since #1365 converts extra M/m _coordinates_ to L/l commands, the only consecutive M/m commands at render time are ones that were explicitly defined as M/m in the path. Those should be treated as moveto commands, even if it means nothing will be drawn.

Example:
```xml
<?xml version="1.0"?>
<svg width="400" height="400" viewBox="0 0 400 400" xmlns="http://www.w3.org/2000/svg">
  <path d="M 50,175 175,50 M 200,175 M 225,50 L 350,175 M 225,200 m 125,25 -125,125 m -25,-125 m -25,125 l -125,-125 m 125,-25 M 50,175 Z"
    fill="red" stroke="black" stroke-width="10" />
</svg>
```

**Chrome**:
![explicit-moveto-chrome](https://cloud.githubusercontent.com/assets/887005/3202505/653c4f00-ed91-11e3-9ec5-969cd9380c8f.png)

**Fabric 1.4.6 (before #1365)**:
![explicit-moveto-1 4 6](https://cloud.githubusercontent.com/assets/887005/3202563/f908f706-ed91-11e3-96bf-b3a8b21dbede.png)

**master (with #1365 merged)** (this avoids rendering a few of the lines, but only as a side effect of the parser having converted some of the path nodes to L/l commands):
![explicit-moveto-1365](https://cloud.githubusercontent.com/assets/887005/3202562/f079a2f2-ed91-11e3-852f-ecb798b796ea.png)

**Fixed**:
![explicit-moveto-fixed](https://cloud.githubusercontent.com/assets/887005/3202646/a1decf18-ed92-11e3-9d76-8bc15844a45c.png)