added blastIndexDirs argument to BlastDB, moved checkDB() step to blast and megablast methods.
added blastIndexDirs argument to BlastDB, moved checkDB() step to
blast and megablast methods.

ctb/pygr,ctb/pygr,theoryno3/pygr,GenDataPro/pygr,RitwikGupta/pygr,GenDataPro/pygr,theoryno3/pygr,ctb/pygr,cjlee112/pygr,RitwikGupta/pygr,cjlee112/pygr,RitwikGupta/pygr,ctb/pygr,theoryno3/pygr,cjlee112/pygr,GenDataPro/pygr,cjlee112/pygr,ctb/pygr