imfile: Initial implementation of solaris FEN API (without wildcards)
FEN API is used to implement simular event based file
monitoring like with inotify.
This commit provides partial functionality. It supports event-driven
processing of files but does not yet provide wildcard functionality.
Wildscards will be provided by a later commit.
This can be committed as-is because the previous code did also
not provide wildcard support, so this is an improvement for
Solaris in any case.
see also https://github.com/rsyslog/rsyslog/issues/1954
