Avoid writing malformed output when the positions are too large.
fix negative sign issue, and gracefully degrade precision by lopping off decimal places
change error
Merge pull request #20 from rmcgibbo/pdb-overflow

Avoid writing malformed PDBs when the positions are too large.
Merge branch 'master' of https://github.com/SimTk/openmm
Python wrapper for getVirtualSite() returns the correct subclass
Fixed bugs in addExtraParticles()
Merge branch 'pme' of https://github.com/peastman/openmm into pme
Merge branch 'pme' of https://github.com/peastman/openmm into pme
Fixed compilation errors on Linux