schema_change: pipeline_wide_parameters added instead of meta for clearer separation
schema_change: remove the 'monitor' table in favour of generate_timeline.pl script
new schema (v.58) diagram
bugfix [to 665ea6c] : properly parse param_hash from MetaAdaptor
api_change: moved caching of MetaParameters and PipelineWideParameters into Cacheable
bugfix: make sure substitutions mentioned in show_useful_commands are actually substituted
allow both compared entities to be undefined (two undefs considered equal)
Cacheable classes support unique index within each collection to avoid creating+adding duplicates
support multiple -pipeconfig options (each applied on top of the previous state of the graph)
cleanup: hashed_by_dbID() method is not really used
bugfix [to 4078bd6] : do not print the legend on the first pass
-hive_no_init : a quick way to switch off pipeline_create_commands ( NB: not specific to a particular -pipeconfig )