Distinguish between 'add' and 'lighter'

When CAIRO_OPERATOR_ADD and CAIRO_OPERATOR_LIGHTEN are both available,
make CAIRO_OPERATOR_ADD available as 'add'.
Release 1.1.5
travis: test node v0.6, v0.8, v0.10, and v0.11
travis: attempt to run the ./install script before testintg
install: use more compatible sh syntax
install: install `giflib`
install: use an older version of giflib (v4.2.3)

v5.x.x seems to make node-canvas fail to compile :(
Needs compat updating...
install: use an even older version of giflib (v4.1.6)

This matches what Homebrew is currently installing...
Giflib 5.1

update to compile with giflib >= 5.1
Update Image.cc
Update Image.h
Giflib 5.1
Glib version test into giflib exists test

Include test of glib version into the have gif lib test
export canvas.CanvasPixelArray instead of canvas.PixelArray which is undefined
Merge pull request #447 from svandecappelle/master

giflib 5.1
Merge pull request #448 from Gottox/master

export canvas.CanvasPixelArray instead of canvas.PixelArray which is undefined
Merge pull request #381 from mojodna/add-operator

Distinguish between 'add' and 'lighter'
Include pre-built binaries in published package.