mappings/VegCSV-VegBIEN.specimens.csv: Cleaned up using `make mappings/`

schemas/functions.sql: join_strs_transform(): Use STRICT optimization to avoid needing to manually check if the state value or input value is NULL (http://www.postgresql.org/docs/8.3/static/sql-createaggregate.html#AEN51596)

schemas/functions.sql: join_strs(), join_strs_transform(): Reversed order of params to enable strict optimization, which replaces the state value with the first parameter, which used to be the delimiter (http://www.postgresql.org/docs/8.3/static/sql-createaggregate.html#AEN51596)

Renamed join_strs_transform_preserve_empty() to join_strs_transform() now that there are no other join_strs_transform_...() functions

schemas/functions.sql: Removed no longer used join_strs_transform_fold_empty()

schemas/functions.sql: join_strs() aggregate: Use join_strs_transform_preserve_empty() as an optimization because all our data has already had '' replaced with NULL by sql_io.cleanup_table() in csv2db. This will help speed up _merges now that they are performed on a large scale in the slowest datasource, SpeciesLink.

bin/map: collision_suffix: Changed to use _merge instead of _alt to avoid losing source data on import when multiple fields collide

bin/map: Preventing collisions if multiple inputs mapping to same output: Made collision suffix configurable so it can easily be changed

bin/map: Preventing collisions if multiple inputs mapping to same output: Made collision suffix configurable so it can easily be changed

mappings/DwC2-VegBIEN.specimens.csv, VegCSV-VegBIEN.specimens.csv: taxonoccurrence.sourceaccessioncode mappings: Added catalogNumber mapping, which takes precendence over recordNumber and is applicable to specimens data and direct vouchers. recordNumber should only be used as a last resort (before the taxon name) because this is collector-assigned and often not unique within anything.