ERT-727: Added refcase explicitly to the time_map

The refcase will only be added if the time mappings of the refcase are
consistent with what is already in the time_map.
ERT-727: Explicitly initialized logh to NULL.
ERT-727: Added numeric test on log_level

By explicitly checking that log_level > 0 we can instantiate a logh
object on a read only filesystem if we set the log_level to 0 zero.
ERT-727: Changed initialization of log handle.
ERT-727: Moved log_include_message() check
ERT-727: Added logging to time_map update
ERT-727: Added function @TYPE@_vector_iset_block()
ERT-727: Added function @TYPE@_vector_resize()
ERT-727: Changed summary load to use time_index

The loading of summary vectors has been changed:

 1. The time_map_summary_update() is called before the actual loading
    starts.

 2. The enkf_node_forward_load() function takes a time_index mapping
    from internal (time) storage index to summary report step; this
    mapping is created by the time_map. As part of this rewrite the old
    [load_start:load_end] convention has been removed.