add code to read/write data in MapQTL format
read.cross.mq: Fix typo (lentgh -> length)
Small change in read.cross.mq: less -> fewer
Update version; add Timothee Flutre to author list in DESCRIPTION
write.cross.mq: slightly more detail in error message
read.cross.mq (mapqtl format): fix two bugs

 - was reordering chromosomes

 - was turning phenotypes into numeric indices and losing actual
   phenotype data
.Rbuildignore: ignore tests/.RData and tests/.Rhistory
Add tests of mapqtl input/output