BF: rename _ as _junk when not intended as translation function _( )

- need to avoid name collision in the app: use of _ to mean junk when unpacking tuple, vs global translation function
- only preferences.py should actually matter, maybe info.py (because the translation function is for the app, not user scripts)
- but change everywhere to be consistent

$ find ../.. -name '*.py' | xargs -n 1 python gg_.py > gg_out.txt

# where gg_.py is:
import re, sys
exp = re.compile(r'\b_\b[^\(]')
print sys.argv[1], '---------'*4
for i,line in enumerate(open(sys.argv[1]).readlines()):
  if exp.search(line):
    print i+1, ':', line,