py2.6 compat
Fix Issue #529: Test for 64bit OS, plus consequential documentation changes
Reflect review comments on the documentation changes
Revise location of 64-bit operating system check to build_ext
Convert to DistutilsPlatformError, for reporting non 64-bit operating systems
Update ChangeLog
Resolve make pep8 line length warning
Merge pull request #581 from ged-lab/fix/579py2.6

py2.6 compat
Merge branch 'fix/issue_529' of github.com:Echelon9/khmer into Echelon9-fix/issue_529
Merge branch 'Echelon9-fix/issue_529'