Merge from vendor branch GROFF:

Merge from vendor branch GROFF:
Update to groff 1.19.2.

With the following changes:

pic: The by argument in a for loop can now be negative if it is additive. For
     the multiplicative case, it must be greater than zero.

eqn: document the keywords: undef NAME, copy "FILE", space n.
eqn: document the macros: Alpha, ..., Omega, ldots, dollar.
eqn: document extended keywords: col n { ... }, lcol n { ... },
     rcol n { ... }, ccol n { ... }, pile n { ... }, lpile n { ... },
     rpile n { ... }, cpile n { ... }

grohtml: This device driver has been raised to beta stage; its set of tags
         should be stable now.
grohtml: New command line option s to set the base point size.
grohtml: New command line option S to set the split level while generating
         multiple files.

grotty: Experimental support for zero-width and double-width characters.

pdfroff: A new wrapper script contributed by Keith Marshall to easily create
         PDF documents with groff.

And some smaller changes.