Added thin type local_obsdata_node
Added is_instance() function to @type@_vector - made safe_cast() static
Removed mode argument in constructor + added is_instance functionality
Added content to local_obsdata_node
Added (empty) container local_obsdata
Added (empty) type obs_tstep_list
local_obsdata_node uses obs_tstep_list instead of plain int_vector
Fixed bug in @TYPE@_vector_index() for empty vector
obs_tstep_list will mantain a sorted list of unique tstep; added iget++
local_obsdata - a vector of local_obsdata_node instances
Added active_list_equal() function
Added active_list_copy() function
Added code manipulate the active_list content of obsdata_node
Added add_tstep() method to local_obsdata_node type
Added obs_tstep_list_get_last()
Minor bug with incorrect error message
Reimplement enkf_obs_get_obs_and_measure() to use local_obsdata and local_obsdata_node internally
Merge branch 'master' into PCA-plot
Refacotoring:
 1) enkf_obs_get_obs_and_measure() based on iterating over
    enkf_obs_get_obs_and_measure_node().
 2) Splitting enkf_main_get_PC -> enkf_main_get_PC + enkf_main_fprintf_PC()
Merge branch 'master' into PCA-plot