WebSearch: handling journal and colon searches
- in SPIRES parser, journal searches with colon internally are now correctly parsed into commas instead
- in SPIRES parser, better handling of journal searches, i.e. f j physics 0903 024 now becomes journal:physics,0903,024 rather than journal:physics and journal:0903 and journal:024
- in search_engine, if an index with fewer than two characters (e.g. '1' or 'a') is queried, search instead in anyfield, without generating user-facing exceptions
- more rigorous check for length of fields in search_unit_in_bibxxx
- tests for same (fixes #669)