Extend Filesystem::searchpath_find() to be able to search recursively.
Basic text rendering into images with ImageBufAlgo::render_text and oiitool --text
Fix DPX output endianness problem for 16 bit DPX output (issue 354)
Add test for regression of issue 354 - 16 bit DPX output endian problems
Merge pull request #392 from lgritz/lg-text

Basic text rendering into imges with ImageBufAlgo::render_text and oiitool --text
TextureSystem: Fixes fill_channels when a monochrome image with alpha has to be expanded to 4 channels
Fix typo that led to bug in get_pixel_channels (from a recent change)
Beef up error reporting mechanism for ImageBuf.
* Add public error(...) so app code can associate an error with an ImageBuf.
* Thread safety for IB error handling.
New convention for ImageBufAlgo error reporting: call error() on Result ImageBuf.
Implement this for IBA::render_text and collect it properly via oiiotool.
Wide deployment of new IB/IBA/oiiotool error reporting scheme
Fix typo preventing searchpath_find from working recursively.
Merge pull request #407 from lgritz/lg-errors

ImageBuf error reporting beef-up
Add Strutil::strip()
Change recent ImageBuf addition -- I don't like spin_mutex being in the public
definition of ImageBuf.  Move the mutex to be static in imagebuf.cpp, not in
the header.  That also eliminates the need for imagebuf.h to include thread.h.
Histogram calculation in ImageBufAlgo and oiiotool

Here we add two new ImageBufAlgo public functions:

* ImageBufAlgo::histogram      - Compute histogram, and store in a
                                 vector of counts
* ImageBufAlgo::histogram_draw - Draw histogram into an ImageBuf

Also included is an oiiotool interface which allows the user to generate
histograms of a specified channel and draw the result into an image.
Error printing for histograms
histogram tests
Fix many compiler warnings and beef up I/O error checking:
* Many cases where we were ignoring the results of fread or fwrite, so
  now we religiously check the results and set errors appropriately
  (this affected bmp, fits, ico, jpeg2000, sgi, targa, tiff, webp, zfile).
* Some unused variables.
This work was mostly Kevin Brightwell, with a cleanup pass by Larry Gritz.
Fix missing OpenEXR open() error message; clean up error reporting in iconvert.
iv refactoring: Split IvGL class definition into ivgl.h (from imageviewer.h).