Fix missing return in ImageBugAlgo::flatten().
Fix ImageCache::get_pixels() for chbegin != 0 case.

The source data channel offset was being applied using the size of the destination datatype rather than from size of the source datatype.

Fixes #759.
Update ref image after recent 'flash explanation' change
DPX bug fix -- inappropriate use of "dpx:ImageDescriptor" could make invalid files.

A simple recipe for disaster was
  "oiiotool rgba.dpx --ch R,G,B -o rgb.dpx"
You'd think this would simply strip the alpha from an RGBA file, but
rgba.dpx reported a "dpx:ImageDescriptor" metadata of "RGBA", which when
propagated to rgb.dpx made it produce a file that looked like it still
had 4 channels.  Oops.

So this patch ignores the "dpx:ImageDescriptor" metadata upon output, instead
generating the output descriptor based on the number of channels (and in some
cases, refining if the channel names suggest a specific standard interpretation).
CHANGES and docs updates
Rebuild PDF docs
Bump version to 1.4.1
Fix Software attribute for dpx output
Fix exr bug with stringvector attributes in the file
We get the data as std::string[] from IlmImf, but it needs to be char*[] for the
ImageSpec.
Fix build break for OpenEXR 1.x
Fix warning with g++ 4.8 and Boost Python
CHANGES updates
Read more Exif metadata from raw files by attempting to open the file as a TIFF
and copying any Exif data we find -- which surprisingly works for quite a few
raw formats.
build warning fixes
EXR: Added sxr and mxr as possible extensions
fixed compiler warnings
string_ref helper class encapsulates a char* and length without ownership.

This is really helpful for passing string arguments to functions that
need to examine the contents of a string but do not themselves need to
own it.  You can uniformly pass any of char* or std::string or a string
array.  it will do so without allocation or copying.

This is very similar to the string_ref that has been proposed by the
C++0y standard (but for which we can't count on uniformly available
compiler support for many years).
use string_ref where helpful in Strutil and ustring.
string_ref amendments to ustring construction
use string_ref for filesystem