Vipscache_operation_buildp

Look up operation in the cache. If we get a hit, unref operation, ref the old one and return that through the argument pointer.

If we miss, build and add operation.

Operators that have been tagged as invalid by VipsImage::invalidate are removed from cache.

Operators with the VIPS_OPERATION_BLOCKED flag are never executed.

Operators with the VIPS_OPERATION_REVALIDATE flag are always executed and any old cache value is replaced.

Operators with the VIPS_OPERATION_NOCACHE flag are never cached.

This function is not directly available to language bindings.