add descs storage to reads2twobit
fix 32 bit issues

fixes genometool/genometool#214
implement disk-based descs tmp storage in reads2twobit
splint fixes
modify some options of rdj prefilter
scan-build fix reads2twobit
Merge pull request #218 from Garonenur/dw32

fix 32 bit issues
Merge pull request #220 from ggonnella/rdj_descs

handle descriptions in reads2twobit