second-stage/programs/features: Minor updates to parallel tools
combine-feature-counts: fix option parsing
parallel-extract-nfeatures.cc, parallel-extract-spfeatures.cc: more
    status messages, option parsing cleanups
second-stage/programs/prepare-data: ptb can now read gzip/bzip files
Duplicating popen.h is unfortunate but is necessary until there's some
reorganization (adding features/ as an include directory causes some
other issues).
first-stage/PARSE: Eliminate maximum word length constraint and assertion
The lowercasing function which previously imposed this constraint has been
rewritten. As bonuses, we now use clocale and have fewer conversions between
C/C++ strings, and can remove our toLower function.
regression-test: Minor text updates