I used cppcheck --enable=all.

When using IFile or OFile only, it is sufficient to include
one of the two header files.

Also, consistently:
PlumedIFile -> IFile
PlumedOFile -> OFile
PlumedFileBase -> FileBase

The guard "ifndef/define" has been updated so as to also include the
module name. This is important as it will allow files with the same name
to be used in different directories. Modification was done automatically
using header.sh - just run it routinely to keep names consistent