Log Message:
ilmbase, openexr: Update to 2.5.1

Changelog:
2.5.1:

A patch release that corrects the SO version for the v2.5 release, which missed \ 
getting bumped in v2.5.0.

This release also fixes an improper failure in IlmImfTest when running on ARMv7 \ 
and AAarch64.

2.5.0:
Minor release with miscellaneous bug fixes and small features

## Summary

* No more build-time header generation: toFloat.h, eLut.h,
  b44ExpLogTable.h, and dwaLookups.h are now ordinary header files, no
  longer generated on the fly.
* New StdISSTream class, an "input" stringstream version of StdOSStream
* New Matrix22 class in Imath
* Chromaticity comparison operator now includes white (formerly ignored)
* Various cmake fixes
* Bug fixes for various memory leaks
* Bug fixes for various invalid memory accesses
* New checks to detect damaged input files
* OpenEXR_Viewers has been deprecated, removed from the top-level
  cmake build and documentation.