v3.4.15 fixes two memory issues when parsing IDManifests. Corrupt
or maliciously formed OpenEXR images could trigger excessive memory
allocation, but only in code which decodes the idmanifest attribute.
Other code is unaffected, even when handling files with idmanifest attributes

CVEs have been requested for these issues.

This release also fixes a missing export for Windows builds, and reduces
compiler warnings when compiling example code.