Merge lp://qastaging/~victor-mireyev/simple-scan/484616 into lp://qastaging/~simple-scan-team/simple-scan/trunk

Can you remove the JpegWriter class back to how it was? It doesn't seem to add anything and it makes it harder to review.

Please correct the whitespace before the '(' in the use of functions.

Other than that, looks good.

Is this an enum? Can you put the enum values into the .vapi if so?
+ info.density_unit = 1;

As you can see, there are three important changes:
1) optional density parameter is added
2) n_written parameter is removed as it's trivially obtained via jpeg_data.length
3) Quality and density code is added
92+ info.set_quality (90);
93 + if (density != null)
94 + {
95 + info.density_unit = 1;
96 + info.X_density = (uint16) density;
97 + info.Y_density = (uint16) density;
98 + }

There are two reason for existance of JpegWriter class.

1) JPEG compression code doesn't use any nonstatic methods or properties of the Book class.
2) As JPEG compression code is used in both Book and Page classes, it shouldn't be duplicated.

Do you propose make compress_jpeg method static?