This is a fix for:
vtk/vtk#14310

Windows applications that run for a long time report that rendered
objects do not change. This is because the modified time on a Windows
system is 32 bits. This causes overflows that defeat the modified time
mechanism. This patch defines a new type, vtkMTimeType that is 64
unsigned integer regardless of the architecture.

A mechanism to provide backward compatibility is introduced. The
preprocessor define "VTK_HAS_MTIME_TYPE" can be used in applications
that must build against VTK versions that use the "unsigned long" type
for MTime's.

Methodology used to find MTime occurences:
1) Identify files as follows:
   git grep "unsigned long" | grep ime | cut -d":" -f1,1 | sort | uniq
2) Hand edit each of those files replacing "unsigned long" with
   "vtkMTimeType" where appropriate.
3) Temporarily change typedef for vtkMTimeType to "double" to detect
   missing conversions