Factorize the coordinate generation in map_warp.

This fixes several texture test cases failures in Windows due to a bug in the MSVC optimizer,
which was not generating correct code for map_warp with the optimizations enabled.
Fix double-to-float downcast warnings in testtex.
Update testsuite ref image after recent testtex change
IBA::nonzero_region returns the "shrink wrapped" pixel data window
that excludes black boundary pixels.
oiiotool --autotrim shrinks pixel window to trim black pixels before output
CHANGES, docs, bump version for final 1.2.0 release
Improve docs -- esp. thorough documentation of IBA.
Also some minor fixes and clarifications to comments in imagebufalgo.h
Fix compiler warnings with large unsigned value in test
oiiotool --help should be a success error code, not a failure.
oiiotool: fix help message for --ociolook