Fixing line height for multiline LabelTTF and overlapping pixels in Canvas browsers

Sorry these are combined into 1 request, didn't realize Github wouldn't let me create 2 pull requests from 1 branch.

1st commit:
multiline LabelTTF's were accounting for line spacing in their contentSize calculation, but when it came to actually drawing they were using the raw fontSize for the height.  This change calculates drawing position using the total character height including line spacing instead of the fontSize's raw height.

2nd commit:
when drawing in a non-webGL browser, scale9Sprites were sometimes getting a 1 pixel overlap between the center and right sprites (and presumably the center and top).  This change manually controls the rounding to ensure the edges will always line up, instead of trusting canvas rounding.