pulled in changes from first branch
fixed try horked by merge
separate function for normalize, raise IOError on paired read fail
added backup hashes every save_frequency files
added warning to end of execution when force is true
changed exit code to -1
added force test for normalize-by-median
fixed some undefined variable errors caused by splitting off normalize function
tests working, fixed up normalize args
final commit before push
fixed a typo in the help for -d option
broke off handling into seperate function, standardized string formatting to use newest version
added ht test to test_normalize_by_median_force
added ht kmer existence test to test_normalize_by_median_dumpfrequency
fixed borked percent output
last formatting fix for percentage kept output
updated default desired coverage to 10
updated usage description in docs
Merge branch 'bleeding-edge' of github.com:ged-lab/khmer into graceful-fail2

Updating graceful-fail2 before final pull request into ged-lab
added usage examples to docs