RIL -> RISIB, RISELF
RIL -> RISELF, RISIB
parse_genotype_ids for BC, RISELF, RISIB
BC needs 3 symbols (in case of X chromosome)

 - Also, throw exceptions if insufficient symbols
diff't default genotype_ids for diff't crosses
Merge branch 'master' of git://github.com/pjotrp/qtlHD
Add function to grab a subset of phenotype columns

 - e.g., to perform genome scan on just a subset of phenotypes
Add additional command-line arguments to scanone

 - phencol: phenotypes columns to use for genome scan
 - sex: name of phenotype corresponding to sex
 - crossdir: name of phenotype corresponding to cross direction
Slight improvements in foreach loops in create_phenotype_batches
Another slight improvement in a foreach loop
Clean up code to grab command-line arguments
Add stand-alone scanone to 'rake test_all'