Always specify custom tick marks on non-log-scale.

User-specified tick marks should be specified as
numbers, not exponents, even when log-scaling is
requested for a particular axis. This commit
creates log-scaled tick locations required by
vtkAxis when log scaling is active.

Change-Id: I17bfa2f7178de5c81645ec182d38cdc3338e8a5e
Merge topic '13951_log_custom_ticks' into next

b800566 Always specify custom tick marks on non-log-scale.