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
add cleanindexes target
use cleanindexes target
check for gtlib loadability before running gtruby/gtpython tests
Merge pull request #221 from satta/python-3264

only run scripting language tests when possible
remove debug output
Merge pull request #222 from satta/python-3264

remove debug output
cosmetics
fix documentation for testing
Merge pull request #223 from Garonenur/dw

small cosmetics
gt encseq info:
tests and bugfix for n50 values
gt encseq info
previous n50 value is in fact l50-count
print n50 as min.length of largest sequences covering 50% of total seq-length
gt encseq info
remove unused variable "n50_count"
touches genometools/genometools#216