[bugfix] Switch UMFPack complex number branch to long size type
The index type used for UMFPack was recently switched to long int
!291 (closed). However, the specialization of the method
dispatcher for std::complex was not adapted.
The index type used for UMFPack was recently switched to long int
!291 (closed). However, the specialization of the method
dispatcher for std::complex was not adapted.