set fill_id to zero at initialization; Coverity CID 1054789 redux
demote nose & sphinx to extra dependencies.

Auto-install Python developer tools as needed
new khmer/file module

check_file_status(file_path), check_space(in_files),
check_space_for_hashtable(hash_size), check_valid_file_exists(in_files)

Squash support added & import and usage of file have been updated in all scripts under
scripts/
don't implicitly downcast tagset_size()

Changes fileformat version for saved tagsets
formatting only; astyle -A10 lib/counting.{cc,hh}
more downcast removal; scope reduction; prefix oper
force 64bit-only builds on OSX