ERT-727: Added UTIL_SAFE_CAST_HEADER() to vector.h
ERT-727: Added internal strict state to time_map

Previously there were two different functions to update a time_map:
time_map_update() and time_map_update_strict(). If the time_map_update()
function failed it would return false, whereas the
time_map_update_strict() would call util_abort().

With this change the time_map_update_strict() function has been removed,
and the behaviour with respect to failed updates is governed by an
internal strict flag; the default behaviour is strict semantics.
ERT-727: Added function @TYPE@_vector_range_fill()
ERT-727: New function time_map_alloc_index_map()
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.
ERT-727: Will attach refcase when mounting enkf_fs
ERT-727: Added time_map_try_update() functions

These functions were added to be able to call the time_map_update()
functions with illegal arguments and no side effects, even in strict
mode. The purpose is to be able to raise an exception in Python instead
of a low level util_abort().
ERT-727: Extended Python time_map implemntation
Removed argument in time_map_alloc() call

Change after review: time_map_alloc() takes no arguments, removed it
ERT-727: Changed test ert_util_logh.c to accomodate that a logh object can be allocated on a read-only filesystem by setting loglevel to 0
ERT-727: Class TimeMap does no longer throw NotImplementedError - is implemented
ERT-727: Method enkf_mount_alt_fs(): Take into account that param create can be false, and new_fs can be NULL