bugfix: schemas/Makefile: $(confirmRmPublicSchema): only prompt to delete the schema if it actually exists. this avoids prompting to remove a non-existent schema at the beginning of bin/import_all, which requires user attention. since bin/import_all is often run with a delayed start (e.g. to wait for a staging table reinstall to complete), the user may not be at the terminal when this message is displayed, and without this fix, the import would be prevented from running until they return.

inputs/.geoscrub/geoscrub_output/run: import() runtime: added starscream runtime (20 min)

planning/timeline/timeline.2013.xls: updated for progress

inputs/.geoscrub/geoscrub_output/run: documented import() runtime (15 min)

inputs/.geoscrub/Source/map.csv: source__modified_date: updated for current run

**/new_terms.csv, unmapped_terms.csv updated (using `make missing_mappings`)

/README.TXT: Full database import: documented that `make schemas/reinstall` requires sudo access

inputs/.geoscrub/geoscrub_output/geoscrub.csv.run: updated upload time (30 s)

inputs/.geoscrub/geoscrub_output/geoscrub.csv.run: export_(): updated runtime (25 s)

lib/sh/util.sh: import_vars: don't overwrite vars that are already defined, to allow the caller to specify their own values for the vars to create. this requires callers that rely on the overwriting functionality to reverse the order in which they run use_* commands, so that the higher-precedence use_* is applied first and the other one as the default values for the first.