surface: support get/set device scale
surface test: add device_scale test
exception: add exception to `Jbig2GlobalMissing`
exception test: add `Jbig2GlobalMissing` test
surface: add missing space
surface: add missing spaces

It also needs space:
rb_float_new (
            ^
            This position.
surface: remove needless parenthese
quartz_image_surface: add missing include for Cairo::QuartzImageSurface
quartz_surface test: add Cairo::QuartzImageSurface test
Merge pull request #24 from cosmo0920/support-device-scale

Support device scale

Patch by Hiroshi Hatake. Thanks!!!
test: don't use the same value for x_scale and y_scale

It's better that we use different value for different thing to detect
bugs.
Merge pull request #25 from cosmo0920/support-jbig2-global-missing-exception

Support jbig2 global missing exception

Patch by Hiroshi Hatake. Thanks!!!
Don't capitalize abbreviated word

    Jbig2 ->
    JBIG2
reduce cairo-quartz-image include scope.

Because cairo-quartz-image.h needs only rb_cairo_surface.c.
Merge pull request #27 from cosmo0920/add-quartz-image-include

Add missing cairo-quartz-image.h include

Patch by Hiroshi Hatake. Thanks!!!
Surface#supported?: support "QuartzImage" style type name
test: fix wrong surface name
Fix include position
implement `Cairo::FontFace.quartz_supported?` and use this in test

"Helvetica" is specified in cairo/cairoint.h as follows:

    #define CAIRO_QUARTZ_FONT_FAMILY_DEFAULT  "Helvetica"
this definition is redfined:

	#define CAIRO_FONT_FAMILY_DEFAULT CAIRO_QUARTZ_FONT_FAMILY_DEFAULT

And used in `_cairo_gstate_ensure_font_face()`

    font_face = cairo_toy_font_face_create (CAIRO_FONT_FAMILY_DEFAULT,
                                            CAIRO_FONT_SLANT_DEFAULT,
                                            CAIRO_FONT_WEIGHT_DEFAULT);

and `_cairo_gstate_ensure_font_face()` is used in
`cairo_get_font_face()`.

So it is suitable `Cairo::FontFace.quartz_supported?` definition place
in Cairo::FontFace, isn't it?

implement `quartz?` in CairoTestUtils
Merge pull request #29 from cosmo0920/quartz_p

implement `Cairo::FontFace.quartz_supported?` and use this in test

Patch by Hiroshi Hatake. Thanks!!!