Fixed: related x_resolution, y_resolution
  Fixed: test_density(Image_Attributes_UT) in Image_attributes.rb fails #76
  Fixed: test_x_resolution(Image_Attributes_UT) in Image_attributes.rb fails #81
  Fixed: test_y_resolution(Image_Attributes_UT) in Image_attributes.rb fails #82
Test against ImageMagick 6.6.9, 6.7.7, 6.7.9 and 6.8.9 (both with and without HDRI support).
Reduced excessive test matrix size for non-essential builds.
Fixed: removed tests for the default value
ImageMagick now using releases directory.
Merge pull request #102 from u338steven/patch-6

Fixed: related x_resolution, y_resolution
Merge branch 'master' of git://github.com/gemhome/rmagick into patch-5
Fixed: test_colorspace fails (across all versions)