Revision 1293543

Introduced an ImageBuilder helper class, that provides an efficient
setRGB() method. Used it within TIFF: the change reduced the time
taken to load a 20 megapixel file by about 33%, and reduced
the total time taken for the test phase of "mvn package" by 3-4%.
This work is largely based on the patch by Gary Lucas in SANSELAN-56.

Also commented out Debug.purgeMemory() - this method which
sleeps and calls System.gc() should be unnecessary on modern
JVMs, and with it commented out, the time taken for "mvn package"
goes from 1:42 to only 0:44.

Submitted by: Gary Lucas <gwlucas at sonalysts dot com>
Jira issue key: SANSELAN-56