Enable 4-letter resname in PDB output, keeps more pdbinfo.

This still fully adheres to the PDB standard since column 21
is not used by the standard. All common programs (PyMol, VMD, etc)
understand the 4-letter format, and programs that only read three
letters will still read the same filename as they used to. In
particular, this conserves most residue names during pdb<->gro
format conversions. We have also killed the non-standard
wide pdb format to avoid writing broken PDB files.

Fixes #725. Refs #917.

Change-Id: I9b6b8f2e191acdfb65ca2b5d96f39249cd71ea98